1,728 research outputs found
Magnetic and the magnetocaloric properties of Ce1-xRxFe2 and Ce(Fe1-xMx)2 compounds
We have studied selected rare earth doped and transition metal doped CeFe2
compounds by examining their structural, magnetic and magneto-thermal
properties. With substitution of Ce by 5 and 10% Gd and 10% Ho, the Curie
temperature can be tuned to the range of 267-318 K. Localization of Ce 4f
electronic state with rare earth substitutions is attributed for the
enhancement of Curie temperature. On the other hand, with Ga and Al
substitution at the Fe site, system undergoes paramagnetic to ferromagnetic
transition and then to an antiferromagnetic phase on cooling. The
magnetocaloric effect across the transitions has been studied from both
magnetization isotherms and heat capacity data. It is shown that by choosing
the appropriate dopant and its concentration, the magnetocaloric effect around
room temperature can be tuned.Comment: 13 pages, 6 figures, 2 table
Observation of re-entrant spin glass behavior in (Ce1-xErx)Fe2 compounds
Clear experimental evidence of re-entrant spin glass state has been revealed
in Er doped CeFe2 compounds. The zero field cooled - field cooled bifurcation
in dc magnetization, frequency dependence of freezing temperature, relaxation
in zero field cooled magnetization and presence of large remanence confirm the
spin glass state in these compounds. Frequency dependence is found to follow
the critical slowing down mechanism. The random substitution of Er and the
change in the valence state of Ce along with an enhancement of the
ferromagnetic component in the Fe sublattice seem to be responsible for the
spin glass state. Using detailed experimental protocols, we also prove that the
low temperature state in these compounds is not a magnetic glass. The absence
of exchange bias gives an indication that there is no coexistence of
ferromagnetism and spin glass state in these compounds. The RSG state is found
to be associated with the randomly magnetized clusters instead of atomic level
randomness.Comment: 19 pages, 9 figure
Applying Deep Learning To Airbnb Search
The application to search ranking is one of the biggest machine learning
success stories at Airbnb. Much of the initial gains were driven by a gradient
boosted decision tree model. The gains, however, plateaued over time. This
paper discusses the work done in applying neural networks in an attempt to
break out of that plateau. We present our perspective not with the intention of
pushing the frontier of new modeling techniques. Instead, ours is a story of
the elements we found useful in applying neural networks to a real life
product. Deep learning was steep learning for us. To other teams embarking on
similar journeys, we hope an account of our struggles and triumphs will provide
some useful pointers. Bon voyage!Comment: 8 page
Enhanced sampling molecular dynamics simulations correctly predict the diverse activities of a series of stiff-stilbene G-quadruplex DNA ligands
Ligands with the capability to bind G-quadruplexes (G4s) specifically, and to control G4 structure and behaviour, offer great potential in the development of novel therapies, technologies and functional materials. Most known ligands bind to a pre-formed topology, but G4s are highly dynamic and a small number of ligands have been discovered that influence these folding equilibria. Such ligands may be useful as probes to understand the dynamic nature of G4 in vivo, or to exploit the polymorphism of G4 in the development of molecular devices. To date, these fascinating molecules have been discovered serendipitously. There is a need for tools to predict such effects to drive ligand design and development, and for molecular-level understanding of ligand binding mechanisms and associated topological perturbation of G4 structures. Here we study the G4 binding mechanisms of a family of stiff-stilbene G4 ligands to human telomeric DNA using molecular dynamics (MD) and enhanced sampling (metadynamics) MD simulations. The simulations predict a variety of binding mechanisms and effects on G4 structure for the different ligands in the series. In parallel, we characterize the binding of the ligands to the G4 target experimentally using NMR and CD spectroscopy. The results show good agreement between the simulated and experimentally observed binding modes, binding affinities and ligand-induced perturbation of the G4 structure. The simulations correctly predict ligands that perturb G4 topology. Metadynamics simulations are shown to be a powerful tool to aid development of molecules to influence G4 structure, both in interpreting experiments and to help in the design of these chemotypes
Field induced single molecule magnet behavior in Dy-based coordination polymer
A new mononuclear Dysprosium based Coordination Polymer {Dy-CP} was
investigated magnetically using dc and ac magnetic susceptibility. The dc
magnetic susceptibility does not exhibit any long-range ordering down to 1.8 K
and the negative value of Curie Constant (~ - 4 K) indicate the dominance of
antiferromagnetic interactions between the Dy (III) spins. Ac susceptibility
exhibits absence of single molecular magnet behavior at zero dc magnetic field
and shows signal of quantum tunneling magnetization (QTM) below 8 K. However,
on the superimposition of dc magnetic field (3 kOe), frequency dependent
relaxation peak emerged at T_f = 5 K and QTM signal suppress at higher fields.
The intermediate value of Mydosh parameter calculated from the shift in peak
position (T_f) in ac susceptibility reflects the formation of superparamagnetic
state. Further, the temperature dependence of Tf is analyzed with Arrhenius and
Cole-Cole plot. The magnetic susceptibility analysis yields characteristics
pre-relaxation factor 1.40x10^(-12) sec and energy barrier {\Delta}E/k_B = 93.4
K, indicating the slow spin relaxation. The Cole-Cole fit to the ac
susceptibility data shows further evidence for the single ion spin relaxation.
Thus, the magnetic measurements support the single-molecule magnet behavior in
Dy-CP under the application of dc magnetic field.Comment: 4 pages, 3 figure
Automated Virtual Design of Organic Semiconductors Based on Metal-Organic Frameworks
The arrangement of organic semiconductor molecules in a material can be modulated using different supramolecular approaches, including the metal–organic framework (MOF) approach. These arrangements result in different frameworks topologies and structures. Fabrication of materials comprising optimized assemblies and functional molecules enables efficient tailoring of material properties, including electronic responses. Since semiconducting properties are sensitive to subtle changes in the nanostructure of the material, the exploitation of MOFs has promising potential in the development of new materials with designed structure and function. Based on decade-long method development, virtual design strategies have become ever more important, and such design methods profit from the availability of automated tools. Such tools enable screening of huge libraries of organic molecules in in silico models of the structure of three-dimensional nanoscale assemblies as the prerequisite to predict their functionality. In this report, we present and demonstrate the application of an automated workflow tool developed for MOFs of the primitive cubic (PCU) topology. We use pentacene-based ditopic linkers of a varied chemical composition and pillar linkers of different molecular sizes to automatically generate PCU MOFs, sample their structural dynamics at finite temperature, and predict electronic coupling matrix elements in vibrationally averaged assemblies. We demonstrate the change of the intermolecular ordering in the resulting MOFs and its impact on the semiconducting properties. This development lays the basis of an extendable framework to automatically model a wide variety of MOFs and characterize their function with respect to properties, such as conduction properties, absorption, and interaction with light. The developed workflow protocol and tools are available at https://github.com/KIT-Workflows/PCU-MOF
Identification of the Moving Junction Complex of Toxoplasma gondii: A Collaboration between Distinct Secretory Organelles
Apicomplexan parasites, including Toxoplasma gondii and Plasmodium sp., are obligate intracellular protozoa. They enter into a host cell by attaching to and then creating an invagination in the host cell plasma membrane. Contact between parasite and host plasma membranes occurs in the form of a ring-shaped moving junction that begins at the anterior end of the parasite and then migrates posteriorly. The resulting invagination of host plasma membrane creates a parasitophorous vacuole that completely envelops the now intracellular parasite. At the start of this process, apical membrane antigen 1 (AMA1) is released onto the parasite surface from specialized secretory organelles called micronemes. The T. gondii version of this protein, TgAMA1, has been shown to be essential for invasion but its exact role has not previously been determined. We identify here a trio of proteins that associate with TgAMA1, at least one of which associates with TgAMA1 at the moving junction. Surprisingly, these new proteins derive not from micronemes, but from the anterior secretory organelles known as rhoptries and specifically, for at least two, from the neck portion of these club-shaped structures. Homologues for these AMA1-associated proteins are found throughout the Apicomplexa strongly suggesting that this moving junction apparatus is a conserved feature of this important class of parasites. Differences between the contributing proteins in different species may, in part, be the result of selective pressure from the different niches occupied by these parasites
A novel, high-sensitivity, bacteriophage-based assay identifies low level Mycobacterium tuberculosis bacteraemia in immunocompetent patients with active and incipient tuberculosis
Haematogenous dissemination of M. tuberculosis (Mtb) is critical to pathogenesis of progressive tuberculous infection in animal models. Using a novel phage-based blood assay, we report the first concordant evidence in well-characterised immunocompetent human cohorts, demonstrating associations of Mtb bacteraemia with progressive phenotypes of latent infection and active pulmonary TB respectively
Seismic structure of the lithosphere and upper mantle beneath the ocean islands near mid-oceanic ridges
Deciphering the seismic character of the young
lithosphere near mid-oceanic ridges (MORs) is a challenging endeavor. In
this study, we determine the seismic structure of the oceanic plate near the
MORs using the P-to-S conversions isolated from quality data recorded
at five broadband seismological stations situated on ocean islands in their
vicinity. Estimates of the crustal and lithospheric thickness values from waveform inversion of the P-receiver function stacks at individual stations
reveal that the Moho depth varies between ~ 10 ± 1 km and
~ 20 ± 1 km with the depths of the
lithosphere–asthenosphere boundary (LAB) varying between ~ 40 ± 4 and ~ 65 ± 7 km. We found evidence for an
additional low-velocity layer below the expected LAB depths at stations on
Ascension, São Jorge and Easter islands. The layer probably relates to the
presence of a hot spot corresponding to a magma chamber. Further, thinning of
the upper mantle transition zone suggests a hotter mantle transition zone
due to the possible presence of plumes in the mantle beneath the stations
- …