ring ASI Harjeet Singh promoted as SI for exemplary courage during Patiala Sabzi Mandi attack By www.newkerala.com Published On :: Fri, 17 Apr 2020 15:30:02 +0530 Full Article
ring Punjab CM for strict enforcement of mask wearing By www.newkerala.com Published On :: Sat, 18 Apr 2020 07:55:02 +0530 Full Article
ring 33,000 people enrolled at de-addiction centres in Punjab during lockdown: State Health Minister By www.newkerala.com Published On :: Sat, 18 Apr 2020 10:42:01 +0530 Full Article
ring Punjab to bring 12.5 lakh acres under cotton cultivation By www.newkerala.com Published On :: Sun, 19 Apr 2020 17:56:01 +0530 Full Article
ring Punjab cop recovering, 5 months physiotherapy needed: PGIMER By www.newkerala.com Published On :: Tue, 21 Apr 2020 16:42:01 +0530 Full Article
ring Vegetable farmers bearing brunt of lockdown in Ludhiana By www.newkerala.com Published On :: Fri, 24 Apr 2020 16:21:01 +0530 Full Article
ring SI Harjeet is recovering well: Punjab CM By www.newkerala.com Published On :: Tue, 28 Apr 2020 08:38:01 +0530 Full Article
ring Punjab govt launches competition for students to spread positivity during lockdown By www.newkerala.com Published On :: Thu, 30 Apr 2020 07:28:01 +0530 Full Article
ring Odisha govt.defends move to bring back migrants By www.thehindu.com Published On :: Sun, 10 May 2020 01:30:45 +0530 Every citizen has a legal right to return to their home, says State’s Chief Spokesperson on COVID-19 Full Article Other States
ring Work begins on final stretch of Outer Ring Road By www.thehindu.com Published On :: Sat, 09 May 2020 23:55:02 +0530 Work to construct the final portion of the Chennai Outer Ring Road (CORR) at Padianallur in Red Hills has begun after the government allowed construct Full Article Chennai
ring Stringer held for harassing college girl in Nagercoil By www.thehindu.com Published On :: Sun, 10 May 2020 00:05:11 +0530 The police seized perpetrator’s laptop, mobile phones and storage devices from his house. Full Article Tamil Nadu
ring Coronavirus | West Bengal govt forms teams for surveillance support, monitoring of treatment at hospitals By www.thehindu.com Published On :: Sun, 10 May 2020 09:16:38 +0530 The team members will pay regular visits to these hospitals and send reports to the department, the state government said in an order. Full Article Other States
ring Audit companies exploring digital options to clear lockdown hurdle By www.business-standard.com Published On :: Sun, 10 May 2020 00:28:00 +0530 While many companies are sharing documents digitally, some have also opened their servers to auditors to access the data they require Full Article
ring Covid-19 woes: Phone majors ring in post-lockdown drill as plants reopen By www.business-standard.com Published On :: Sun, 10 May 2020 00:36:00 +0530 On Saturday, Samsung India Electronics, counted among the largest in the space, ushered in over 1,000 workers at its facility in Sector 81, Noida Full Article
ring India plans over 100 flights during second phase of evacuation abroad By www.thehindubusinessline.com Published On :: Sat, 09 May 2020 21:07:28 +0530 To link countries where no Indian carrier presently flies Full Article Logistics
ring Cochin Port Trust helps during ‘Operation Samudra Sethu’ for Maldives expatriates By www.thehindubusinessline.com Published On :: Sun, 10 May 2020 11:55:50 +0530 This is the Indian Navy’s first massive evacuation exercise during the Covid-19 lockdown Full Article National
ring Massive dust storm hits Delhi-NCR; accompanying rains bring relief from summer heat By www.dnaindia.com Published On :: Sun, 10 May 2020 06:40:00 GMT The change in weather and the dust storm was witnessed in areas from Noida to Rajouri Garden in West Delhi. Full Article India
ring Punjab and Haryana HC to hold 10 benches for hearing of urgent cases over video conferencing By indianexpress.com Published On :: Sun, 10 May 2020 03:44:56 +0000 Full Article Chandigarh Cities
ring Device for source position stabilization and beam parameter monitoring at inverse Compton X-ray sources By scripts.iucr.org Published On :: 2019-08-07 Compact X-ray sources based on inverse Compton scattering provide brilliant and partially coherent X-rays in a laboratory environment. The cross section for inverse Compton scattering is very small, requiring high-power laser systems as well as small laser and electron beam sizes at the interaction point to generate sufficient flux. Therefore, these systems are very sensitive to distortions which change the overlap between the two beams. In order to monitor X-ray source position, size and flux in parallel to experiments, the beam-position monitor proposed here comprises a small knife edge whose image is acquired with an X-ray camera specifically designed to intercept only a very small fraction of the X-ray beam. Based on the source position drift recorded with the monitor, a closed-loop feedback stabilizes the X-ray source position by adjusting the laser beam trajectory. A decrease of long-term source position drifts by more than one order of magnitude is demonstrated with this device. Consequently, such a closed-loop feedback system which enables stabilization of source position drifts and flux of inverse Compton sources in parallel to experiments has a significant impact on the performance of these sources. Full Article text
ring Microfluidic electrochemical cell for in situ structural characterization of amorphous thin-film catalysts using high-energy X-ray scattering By scripts.iucr.org Published On :: 2019-08-09 Porous, high-surface-area electrode architectures are described that allow structural characterization of interfacial amorphous thin films with high spatial resolution under device-relevant functional electrochemical conditions using high-energy X-ray (>50 keV) scattering and pair distribution function (PDF) analysis. Porous electrodes were fabricated from glass-capillary array membranes coated with conformal transparent conductive oxide layers, consisting of either a 40 nm–50 nm crystalline indium tin oxide or a 100 nm–150 nm-thick amorphous indium zinc oxide deposited by atomic layer deposition. These porous electrodes solve the problem of insufficient interaction volumes for catalyst thin films in two-dimensional working electrode designs and provide sufficiently low scattering backgrounds to enable high-resolution signal collection from interfacial thin-film catalysts. For example, PDF measurements were readily obtained with 0.2 Å spatial resolution for amorphous cobalt oxide films with thicknesses down to 60 nm when deposited on a porous electrode with 40 µm-diameter pores. This level of resolution resolves the cobaltate domain size and structure, the presence of defect sites assigned to the domain edges, and the changes in fine structure upon redox state change that are relevant to quantitative structure–function modeling. The results suggest the opportunity to leverage the porous, electrode architectures for PDF analysis of nanometre-scale surface-supported molecular catalysts. In addition, a compact 3D-printed electrochemical cell in a three-electrode configuration is described which is designed to allow for simultaneous X-ray transmission and electrolyte flow through the porous working electrode. Full Article text
ring Microsecond time-resolved X-ray diffraction for the investigation of fatigue behavior during ultrasonic fatigue loading By scripts.iucr.org Published On :: 2019-08-20 A new method based on time-resolved X-ray diffraction is proposed in order to measure the elastic strain and stress during ultrasonic fatigue loading experiments. Pure Cu was chosen as an example material for the experiments using a 20 kHz ultrasonic fatigue machine mounted on the six-circle diffractometer available at the DiffAbs beamline on the SOLEIL synchrotron facility in France. A two-dimensional hybrid pixel X-ray detector (XPAD3.2) was triggered by the strain gage signal in a synchronous data acquisition scheme (pump–probe-like). The method enables studying loading cycles with a period of 50 µs, achieving a temporal resolution of 1 µs. This allows a precise reconstruction of the diffraction patterns during the loading cycles. From the diffraction patterns, the position of the peaks, their shifts and their respective broadening can be deduced. The diffraction peak shift allows the elastic lattice strain to be estimated with a resolution of ∼10−5. Stress is calculated by the self-consistent scale-transition model through which the elastic response of the material is estimated. The amplitudes of the cyclic stresses range from 40 to 120 MPa and vary linearly with respect to the displacement applied by the ultrasonic machine. Moreover, the experimental results highlight an increase of the diffraction peak broadening with the number of applied cycles. Full Article text
ring BioStruct-Africa: empowering Africa-based scientists through structural biology knowledge transfer and mentoring – recent advances and future perspectives By scripts.iucr.org Published On :: 2019-08-28 Being able to visualize biology at the molecular level is essential for our understanding of the world. A structural biology approach reveals the molecular basis of disease processes and can guide the design of new drugs as well as aid in the optimization of existing medicines. However, due to the lack of a synchrotron light source, adequate infrastructure, skilled persons and incentives for scientists in addition to limited financial support, the majority of countries across the African continent do not conduct structural biology research. Nevertheless, with technological advances such as robotic protein crystallization and remote data collection capabilities offered by many synchrotron light sources, X-ray crystallography is now potentially accessible to Africa-based scientists. This leap in technology led to the establishment in 2017 of BioStruct-Africa, a non-profit organization (Swedish corporate ID: 802509-6689) whose core aim is capacity building for African students and researchers in the field of structural biology with a focus on prevalent diseases in the African continent. The team is mainly composed of, but not limited to, a group of structural biologists from the African diaspora. The members of BioStruct-Africa have taken up the mantle to serve as a catalyst in order to facilitate the information and technology transfer to those with the greatest desire and need within Africa. BioStruct-Africa achieves this by organizing workshops onsite at our partner universities and institutions based in Africa, followed by post-hoc online mentoring of participants to ensure sustainable capacity building. The workshops provide a theoretical background on protein crystallography, hands-on practical experience in protein crystallization, crystal harvesting and cryo-cooling, live remote data collection on a synchrotron beamline, but most importantly the links to drive further collaboration through research. Capacity building for Africa-based researchers in structural biology is crucial to win the fight against the neglected tropical diseases, e.g. ascariasis, hookworm, trichuriasis, lymphatic filariasis, active trachoma, loiasis, yellow fever, leprosy, rabies, sleeping sickness, onchocerciasis, schistosomiasis, etc., that constitute significant health, social and economic burdens to the continent. BioStruct-Africa aims to build local and national expertise that will have direct benefits for healthcare within the continent. Full Article text
ring White beam diagnostics using X-ray back-scattering from a CVD diamond vacuum window By scripts.iucr.org Published On :: 2020-01-01 Collecting back-scattered X-rays from vacuum windows using a pinhole X-ray camera provides an efficient and reliable method of measuring the beam shape and position of the white synchrotron beam. In this paper, measurements are presented that were conducted at ESRF beamline ID6 which uses an in-vacuum cryogenically cooled permanent-magnet undulator (CPMU18) and a traditional U32 undulator as its radiation sources, allowing tests to be performed at very high power density levels that were adjusted by changing the gap of the undulators. These measurements show that it is possible to record beam shape and beam position using a simple geometry without having to place any further items in the beam path. With this simple test setup it was possible to record the beam position with a root-mean-square noise figure of 150 nm. Full Article text
ring Picosecond pump–probe X-ray scattering at the Elettra SAXS beamline By scripts.iucr.org Published On :: 2020-01-01 A new setup for picosecond pump–probe X-ray scattering at the Austrian SAXS beamline at Elettra-Sincrotrone Trieste is presented. A high-power/high-repetion-rate laser has been installed on-site, delivering UV/VIS/IR femtosecond-pulses in-sync with the storage ring. Data acquisition is achieved by gating a multi-panel detector, capable of discriminating the single X-ray pulse in the dark-gap of the Elettra hybrid filling mode. Specific aspects of laser- and detection-synchronization, on-line beam steering as well protocols for spatial and temporal overlap of laser and X-ray beam are also described. The capabilities of the setup are demonstrated by studying transient heat-transfer in an In/Al/GaAs superlattice structure and results are confirmed by theoretical calculations. Full Article text
ring IRIXS: a resonant inelastic X-ray scattering instrument dedicated to X-rays in the intermediate energy range By scripts.iucr.org Published On :: 2020-02-26 A new resonant inelastic X-ray scattering (RIXS) instrument has been constructed at beamline P01 of the PETRA III synchrotron. This instrument has been named IRIXS (intermediate X-ray energy RIXS) and is dedicated to X-rays in the tender-energy regime (2.5–3.5 keV). The range covers the L2,3 absorption edges of many of the 4d elements (Mo, Tc, Ru, Rh, Pd and Ag), offering a unique opportunity to study their low-energy magnetic and charge excitations. The IRIXS instrument is currently operating at the Ru L3-edge (2840 eV) but can be extended to the other 4d elements using the existing concept. The incoming photons are monochromated with a four-bounce Si(111) monochromator, while the energy analysis of the outgoing photons is performed by a diced spherical crystal analyzer featuring (102) lattice planes of quartz (SiO2). A total resolution of 100 meV (full width at half-maximum) has been achieved at the Ru L3-edge, a number that is in excellent agreement with ray-tracing simulations. Full Article text
ring Beyond simple small-angle X-ray scattering: developments in online complementary techniques and sample environments By journals.iucr.org Published On :: Possibilities in auxiliary technique combinations with small- and wide-angle X ray scattering are described, as well as more complicated sample environments used in X-ray and neutron scattering. Full Article text
ring Correlated changes in structure and viscosity during gelatinization and gelation of tapioca starch granules By journals.iucr.org Published On :: Melting of the semicrystalline structure of native tapioca starch granules is correlated to solution viscosity for elucidating gelatinization and gelation processes. Full Article text
ring Diffuse scattering and partial disorder in complex structures By journals.iucr.org Published On :: This review discusses the state of the field of single-crystal diffuse scattering (SCDS), including detectors, data collection and the modelling techniques. High quality, three-dimensional volumes of SCDS data can now be collected at synchrotron light sources, allowing increasingly detailed and quantitative analyses to be undertaken. Full Article text
ring Investigating increasingly complex macromolecular systems with small-angle X-ray scattering By journals.iucr.org Published On :: A review of recent and ongoing development and results within the field of biological solution small-angle X-ray scattering (BioSAXS), with a focus on the increasing complexity of biological samples, data collection and data evaluation strategies. Full Article text
ring Chemical crystallography and crystal engineering By journals.iucr.org Published On :: Today, there is very little doubt that chemistry owes as much to crystallography as crystallography does to chemistry. This mutual synergy defines modern chemical crystallography. Full Article text
ring Scottish Highlands hit by earthquake with magnitude measuring 2.3 - The Scottish Sun By www.thescottishsun.co.uk Published On :: Tue, 07 Jan 2020 08:00:00 GMT Scottish Highlands hit by earthquake with magnitude measuring 2.3 The Scottish Sun Full Article
ring 'Rumbling' felt during Ardnamurchan earthquake - BBC News By www.bbc.com Published On :: Tue, 17 Mar 2020 07:00:00 GMT 'Rumbling' felt during Ardnamurchan earthquake BBC News Full Article
ring Why the UK's streets have turned silent during coronavirus lockdown - Express.co.uk By www.express.co.uk Published On :: Wed, 29 Apr 2020 07:00:00 GMT Why the UK's streets have turned silent during coronavirus lockdown Express.co.uk Full Article
ring Structure-based screening of binding affinities via small-angle X-ray scattering By scripts.iucr.org Published On :: 2020-05-06 Protein–protein and protein–ligand interactions often involve conformational changes or structural rearrangements that can be quantified by solution small-angle X-ray scattering (SAXS). These scattering intensity measurements reveal structural details of the bound complex, the number of species involved and, additionally, the strength of interactions if carried out as a titration. Although a core part of structural biology workflows, SAXS-based titrations are not commonly used in drug discovery contexts. This is because prior knowledge of expected sample requirements, throughput and prediction accuracy is needed to develop reliable ligand screens. This study presents the use of the histidine-binding protein (26 kDa) and other periplasmic binding proteins to benchmark ligand screen performance. Sample concentrations and exposure times were varied across multiple screening trials at four beamlines to investigate the accuracy and precision of affinity prediction. The volatility ratio between titrated scattering curves and a common apo reference is found to most reliably capture the extent of structural and population changes. This obviates the need to explicitly model scattering intensities of bound complexes, which can be strongly ligand-dependent. Where the dissociation constant is within 102 of the protein concentration and the total exposure times exceed 20 s, the titration protocol presented at 0.5 mg ml−1 yields affinities comparable to isothermal titration calorimetry measurements. Estimated throughput ranges between 20 and 100 ligand titrations per day at current synchrotron beamlines, with the limiting step imposed by sample handling and cleaning procedures. Full Article text
ring Exploring the complex map of insulin polymorphism: a novel crystalline form in the presence of m-cresol By journals.iucr.org Published On :: A novel monoclinic phase of human insulin co-crystallized with m-cresol was structurally characterized by means of powder and single-crystal X-ray diffraction. Full Article text
ring Bis[μ-bis(2,6-diisopropylphenyl) phosphato-κ2O:O']bis[(2,2'-bipyridine-κ2N,N')lithium] toluene disolvate and its catalytic activity in ring-opening polymerization of ∊-caprolactone and l-dilactide By scripts.iucr.org Published On :: 2019-05-21 The solvated centrosymmmtric title compound, [Li2(C24H34O4P)2(C10H8N2)2]·2C7H8, was formed in the reaction between {Li[(2,6-iPr2C6H3-O)2POO](MeOH)3}(MeOH) and 2,2'-bipyridine (bipy) in toluene. The structure has monoclinic (P21/n) symmetry at 120 K and the asymmetric unit consists of half a complex molecule and one molecule of toluene solvent. The diaryl phosphate ligand demonstrates a μ-κO:κO'-bridging coordination mode and the 2,2'-bipyridine ligand is chelating to the Li+ cation, generating a distorted tetrahedral LiN2O2 coordination polyhedron. The complex exhibits a unique dimeric Li2O4P2 core. One isopropyl group is disordered over two orientations in a 0.621 (4):0.379 (4) ratio. In the crystal, weak C—H⋯O and C—H⋯π interactions help to consolidate the packing. Catalytic systems based on the title complex and on the closely related complex {Li[(2,6-iPr2C6H3-O)2POO](MeOH)3}(MeOH) display activity in the ring-opening polymerization of ∊-caprolactone and l-dilactide. Full Article text
ring (1R,2S,4r)-1,2,4-Triphenylcyclopentane-1,2-diol and (1R,2S,4r)-4-(2-methoxyphenyl)-1,2-diphenylcyclopentane-1,2-diol: application as initiators for ring-opening polymerization of ∊-caprolactone By scripts.iucr.org Published On :: 2019-06-21 Reductive cyclization of 1,3,5-triphenyl- and 3-(2-methoxyphenyl)-1,5-diphenylpentane-1,5-diones by zinc in acetic acid medium leads to the formation of 1,2,4-triphenylcyclopentane-1,2-diol [1,2,4-Ph3C5H5-1,2-(OH)2, C23H22O2, (I)] and 4-(2-methoxyphenyl)-1,2-diphenylcyclopentane-1,2-diol [4-(2-MeOC6H4)-1,2-Ph2C5H5-1,2-(OH)2, C24H24O3, (II)]. Their single crystals have been obtained by crystallization from a THF/hexane solvent mixture. Diols (I) and (II) crystallize in orthorhombic (Pbca) and triclinic (Poverline{1}) space groups, respectively, at 150 K. Their asymmetric units comprise one [in the case of (I)] and three [in the case of (II)] crystallographically independent molecules of the achiral (1R,2S,4r)-diol isomer. Each hydroxyl group is involved in one intramolecular and one intermolecular O—H⋯O hydrogen bond, forming one-dimensional chains. Compounds (I) and (II) have been used successfully as precatalyst activators for the ring-opening polymerization of ∊-caprolactone. Full Article text
ring Syntheses and structures of piperazin-1-ium ABr2 (A = Cs or Rb): hybrid solids containing `curtain wall' layers of face- and edge-sharing ABr6 trigonal prisms By scripts.iucr.org Published On :: 2019-07-26 The isostructural title compounds, poly[piperazin-1-ium [di-μ-bromido-caesium]], {(C4H11N2)[CsBr2]}n, and poly[piperazin-1-ium [di-μ-bromido-rubidium]], {(C4H11N2)[RbBr2]}n, contain singly-protonated piperazin-1-ium cations and unusual ABr6 (A = Cs or Rb) trigonal prisms. The prisms are linked into a distinctive `curtain wall' arrangement propagating in the (010) plane by face and edge sharing. In each case, a network of N—H⋯N, N—H⋯Br and N—H⋯(Br,Br) hydrogen bonds consolidates the structure. Full Article text
ring Palladium(II) complexes of a bridging amine bis(phenolate) ligand featuring κ2 and κ3 coordination modes By scripts.iucr.org Published On :: 2019-07-26 Bidentate and tridentate coordination of a 2,4-di-tert-butyl-substituted bridging amine bis(phenolate) ligand to a palladium(II) center are observed within the same crystal structure, namely dichlorido({6,6'-[(ethane-1,2-diylbis(methylazanediyl)]bis(methylene)}bis(2,4-di-tert-butylphenol))palladium(II) chlorido(2,4-di-tert-butyl-6-{[(2-{[(3,5-di-tert-butyl-2-hydroxyphenyl)methyl](methyl)amino}ethyl)(methyl)amino]methyl}phenolato)palladium(II) methanol 1.685-solvate 0.315-hydrate, [PdCl2(C34H56N2O2)][PdCl(C34H55N2O2)]·1.685CH3OH·0.315H2O. Both complexes exhibit a square-planar geometry, with unbound phenol moieties participating in intermolecular hydrogen bonding with co-crystallized water and methanol. The presence of both κ2 and κ3 coordination modes arising from the same solution suggest a dynamic process in which phenol donors may coordinate or dissociate from the metal center, and offers insight into catalyst speciation throughout Pd-mediated processes. The unit cell contains dichlorido({6,6'-[(ethane-1,2-diylbis(methylazanediyl)]bis(methylene)}bis(2,4-di-tert-butylphenol))palladium(II), {(L2)PdCl2}, and chlorido(2,4-di-tert-butyl-6-{[(2-{[(3,5-di-tert-butyl-2-hydroxyphenyl)methyl](methyl)amino}ethyl)(methyl)amino]methyl}phenolato)palladium(II), {(L2X)PdCl}, molecules as well as fractional water and methanol solvent molecules. Full Article text
ring The first crystal structure of the pyrrolo[1,2-c]oxazole ring system By scripts.iucr.org Published On :: 2019-08-23 The title compound, C7H4F3NO2, 3-trifluoromethyl-1H-pyrrolo[1,2-c]oxazol-1-one, is the first crystal structure of the pyrrolo[1,2-c]oxazole ring system: the fused ring system is almost planar (r.m.s. deviation = 0.006 Å). In the crystal, weak C—H⋯O and C—H⋯F hydrogen bonds link the molecules into [001] chains and π–π stacking interactions consolidate the structure. Full Article text
ring The crystal structures of Fe-bearing MgCO3 sp2- and sp3-carbonates at 98 GPa from single-crystal X-ray diffraction using synchrotron radiation By scripts.iucr.org Published On :: 2020-04-21 The crystal structure of MgCO3-II has long been discussed in the literature where DFT-based model calculations predict a pressure-induced transition of the carbon atom from the sp2 to the sp3 type of bonding. We have now determined the crystal structure of iron-bearing MgCO3-II based on single-crystal X-ray diffraction measurements using synchrotron radiation. We laser-heated a synthetic (Mg0.85Fe0.15)CO3 single crystal at 2500 K and 98 GPa and observed the formation of a monoclinic phase with composition (Mg2.53Fe0.47)C3O9 in the space group C2/m that contains tetrahedrally coordinated carbon, where CO44− tetrahedra are linked by corner-sharing oxygen atoms to form three-membered C3O96− ring anions. The crystal structure of (Mg0.85Fe0.15)CO3 (magnesium iron carbonate) at 98 GPa and 300 K is reported here as well. In comparison with previous structure-prediction calculations and powder X-ray diffraction data, our structural data provide reliable information from experiments regarding atomic positions, bond lengths, and bond angles. Full Article text
ring Calculation of total scattering from a crystalline structural model based on experimental optics parameters By scripts.iucr.org Published On :: 2020-05-05 Total scattering measurements enable understanding of the structural disorder in crystalline materials by Fourier transformation of the total structure factor, S(Q), where Q is the magnitude of the scattering vector. In this work, the direct calculation of total scattering from a crystalline structural model is proposed. To calculate the total scattering intensity, a suitable Q-broadening function for the diffraction profile is needed because the intensity and the width depend on the optical parameters of the diffraction apparatus, such as the X-ray energy resolution and divergence, and the intrinsic parameters. X-ray total scattering measurements for CeO2 powder were performed at beamline BL04B2 of the SPring-8 synchrotron radiation facility in Japan for comparison with the calculated S(Q) under various optical conditions. The evaluated Q-broadening function was comparable to the full width at half-maximum of the Bragg peaks in the experimental total scattering pattern. The proposed calculation method correctly accounts for parameters with Q dependence such as the atomic form factor and resolution function, enables estimation of the total scattering factor, and facilitates determination of the reduced pair distribution function for both crystalline and amorphous materials. Full Article text
ring Impact and behavior of Sn during the Ni/GeSn solid-state reaction By scripts.iucr.org Published On :: 2020-04-14 Ni-based intermetallics are promising materials for forming efficient contacts in GeSn-based Si photonic devices. However, the role that Sn might have during the Ni/GeSn solid-state reaction (SSR) is not fully understood. A comprehensive analysis focused on Sn segregation during the Ni/GeSn SSR was carried out. In situ X-ray diffraction and cross-section transmission electron microscopy measurements coupled with energy-dispersive X-ray spectrometry and electron energy-loss spectroscopy atomic mappings were performed to follow the phase sequence, Sn distribution and segregation. The results showed that, during the SSR, Sn was incorporated into the intermetallic phases. Sn segregation happened first around the grain boundaries (GBs) and then towards the surface. Sn accumulation around GBs hampered atom diffusion, delaying the growth of the Ni(GeSn) phase. Higher thermal budgets will thus be mandatory for formation of contacts in high-Sn-content photonic devices, which could be detrimental for thermal stability. Full Article text
ring Sub-millisecond time-resolved small-angle neutron scattering measurements at NIST By scripts.iucr.org Published On :: 2020-04-14 Instrumentation for time-resolved small-angle neutron scattering measurements with sub-millisecond time resolution, based on Gähler's TISANE (time-involved small-angle neutron experiments) concept, is in operation at NIST's Center for Neutron Research. This implementation of the technique includes novel electronics for synchronizing the neutron pulses from high-speed counter-rotating choppers with a periodic stimulus applied to a sample. Instrumentation details are described along with measurements demonstrating the utility of the technique for elucidating the reorientation dynamics of anisometric magnetic particles. Full Article text
ring Structural changes during water-mediated amorphization of semiconducting two-dimensional thiostannates By scripts.iucr.org Published On :: 2019-07-05 Owing to their combined open-framework structures and semiconducting properties, two-dimensional thiostannates show great potential for catalytic and sensing applications. One such class of crystalline materials consists of porous polymeric [Sn3S72−]n sheets with molecular cations embedded in-between. The compounds are denoted R-SnS-1, where R is the cation. Dependent on the cation, some R-SnS-1 thiostannates transition into amorphous phases upon dispersion in water. Knowledge about the fundamental chemical properties of the thiostannates, including their water stability and the nature of the amorphous products, has not yet been established. This paper presents a time-resolved study of the transition from the crystalline to the amorphous phase of two violet-light absorbing thiostannates, i.e. AEPz-SnS-1 [AEPz = 1-(2-aminoethyl)piperazine] and trenH-SnS-1 [tren = tris(2-aminoethyl)amine]. X-ray total scattering data and pair distribution function analysis reveal no change in the local intralayer coordination during the amorphization. However, a rapid decrease in the crystalline domain sizes upon suspension in water is demonstrated. Although scanning electron microscopy shows no significant decrease of the micrometre-sized particles, transmission electron microscopy reveals the formation of small particles (∼200–400 nm) in addition to the larger particles. The amorphization is associated with disorder of the thiostannate nanosheet stacking. For example, an average decrease in the interlayer distance (from 19.0 to 15.6 Å) is connected to the substantial loss of the organic components as shown by elemental analysis and X-ray photoelectron spectroscopy. Despite the structural changes, the light absorption properties of the amorphisized R-SnS-1 compounds remain intact, which is encouraging for future water-based applications of such materials. Full Article text
ring X-ray photon correlation spectroscopy of protein dynamics at nearly diffraction-limited storage rings By scripts.iucr.org Published On :: 2019-07-11 This study explores the possibility of measuring the dynamics of proteins in solution using X-ray photon correlation spectroscopy (XPCS) at nearly diffraction-limited storage rings (DLSRs). We calculate the signal-to-noise ratio (SNR) of XPCS experiments from a concentrated lysozyme solution at the length scale of the hydrodynamic radius of the protein molecule. We take into account limitations given by the critical X-ray dose and find expressions for the SNR as a function of beam size, sample-to-detector distance and photon energy. Specifically, we show that the combined increase in coherent flux and coherence lengths at the DLSR PETRA IV yields an increase in SNR of more than one order of magnitude. The resulting SNR values indicate that XPCS experiments of biological macromolecules on nanometre length scales will become feasible with the advent of a new generation of synchrotron sources. Our findings provide valuable input for the design and construction of future XPCS beamlines at DLSRs. Full Article text
ring Spin resolved electron density study of YTiO3 in its ferromagnetic phase: signature of orbital ordering By scripts.iucr.org Published On :: 2019-08-02 The present work reports on the charge and spin density modelling of YTiO3 in its ferromagnetic state (TC = 27 K). Accurate polarized neutron diffraction and high-resolution X-ray diffraction (XRD) experiments were carried out on a single crystal at the ORPHÉE reactor (LLB) and SPRING8 synchrotron source. The experimental data are modelled by the spin resolved pseudo-atomic multipolar model (Deutsch et al., 2012). The refinement strategy is discussed and the result of this electron density modelling is compared with that from XRD measured at 100 K and with density functional theory calculations. The results show that the spin and charge densities around the Ti atom have lobes directed away from the O atoms, confirming the filling of the t2g orbitals of the Ti atom. The dxy orbital is less populated than dxz and dyz, which is a sign of a partial lift of degeneracy of the t2g orbitals. This study confirms the orbital ordering at low temperature (20 K), which is already present in the paramagnetic state above the ferromagnetic transition (100 K). Full Article text
ring A new small-angle X-ray scattering model for polymer spherulites with a limited lateral size of the lamellar crystals By scripts.iucr.org Published On :: 2019-08-31 As is well known, polymers commonly form lamellar crystals, and these assemble further into lamellar stacks and spherulites during quiescent crystallization. Fifty years ago, Vonk and Kortleve constructed the classical small-angle X-ray scattering theory (SAXS) for a lamellar system, in which it was assumed that the lamellar stack had an infinite lateral size [Vonk & Kortleve (1967), Kolloid Z. Z. Polym. 220, 19–24]. Under this assumption, only crystal planes satisfying the Bragg condition can form strong scattering, and the scattering from the lamellar stack arises from the difference between the scattering intensities in the amorphous and crystalline layers, induced by the incident X-ray beam. This assumption is now deemed unreasonable. In a real polymer spherulite, the lamellar crystal commonly has dimensions of only a few hundred nanometres. At such a limited lateral size, lamellar stacks in a broad orientation have similar scattering, so interference between these lamellar stacks must be considered. Scattering from lamellar stacks parallel to the incident X-ray beam also needs to be considered when total reflection occurs. In this study, various scattering contributions from lamellar stacks in a spherulite are determined. It is found that, for a limited lateral size, the scattering induced by the incident X-ray beam is not the main origin of SAXS. It forms double peaks, which are not observed in real scattering because of destructive interference between the lamellar stacks. The scattering induced by the evanescent wave is the main origin. It can form a similar interference pattern to that observed in a real SAXS measurement: a Guinier region in the small-q range, a signal region in the intermediate-q range and a Porod region in the high-q range. It is estimated that, to avoid destructive interference, the lateral size needs to be greater than 11 µm, which cannot be satisfied in a real lamellar system. Therefore, SAXS in a real polymer system arises largely from the scattering induced by the evanescent wave. Evidence for the existence of the evanescent wave was identified in the scattering of isotactic polypropylene. This study corrects a long-term misunderstanding of SAXS in a polymer lamellar system. Full Article text
ring Engineering a surrogate human heteromeric α/β glycine receptor orthosteric site exploiting the structural homology and stability of acetylcholine-binding protein By scripts.iucr.org Published On :: 2019-09-04 Protein-engineering methods have been exploited to produce a surrogate system for the extracellular neurotransmitter-binding site of a heteromeric human ligand-gated ion channel, the glycine receptor. This approach circumvents two major issues: the inherent experimental difficulties in working with a membrane-bound ion channel and the complication that a heteromeric assembly is necessary to create a key, physiologically relevant binding site. Residues that form the orthosteric site in a highly stable ortholog, acetylcholine-binding protein, were selected for substitution. Recombinant proteins were prepared and characterized in stepwise fashion exploiting a range of biophysical techniques, including X-ray crystallography, married to the use of selected chemical probes. The decision making and development of the surrogate, which is termed a glycine-binding protein, are described, and comparisons are provided with wild-type and homomeric systems that establish features of molecular recognition in the binding site and the confidence that the system is suited for use in early-stage drug discovery targeting a heteromeric α/β glycine receptor. Full Article text
ring Operando X-ray scattering study of thermoelectric β-Zn4Sb3 By scripts.iucr.org Published On :: 2020-01-01 The application of thermoelectrics for energy harvesting depends strongly on operational reliability and it is therefore desirable to investigate the structural integrity of materials under operating conditions. We have developed an operando setup capable of simultaneously measuring X-ray scattering data and electrical resistance on pellets subjected to electrical current. Here, operando investigations of β-Zn4Sb3 are reported at current densities of 0.5, 1.14 and 2.3 A mm−2. At 0.5 A mm−2 no sample decomposition is observed, but Rietveld refinements reveal increased zinc occupancy from the anode to the cathode demonstrating zinc migration under applied current. At 1.14 A mm−2 β-Zn4Sb3 decomposes into ZnSb, but pair distribution function analysis shows that Zn2Sb2 units are preserved during the decomposition. This identifies the mobile zinc in β-Zn4Sb3 as the linkers between the Zn2Sb2 units. At 2.3 A mm−2 severe Joule heating triggers transition into the γ-Zn4Sb3 phase, which eventually decomposes into ZnSb, demonstrating Zn ion mobility also in γ-Zn4Sb3 under electrical current. Full Article text