512 research outputs found
Development of improved thermoelectric mater- ials for spacecraft applications final summary report, 29 jun. 1964 - 29 jun. 1965
Thermoelectric materials for spacecraft applications - optimization of bismuth-antimony alloys and ag-sb-fe-te-se system alloys for thermoelectric cooling in space environmen
Current-Induced Spin Polarization in Gallium Nitride
Electrically generated spin polarization is probed directly in bulk GaN using
Kerr rotation spectroscopy. A series of n-type GaN epilayers are grown in the
wurtzite phase both by molecular beam epitaxy (MBE) and metalorganic chemical
vapor deposition (MOCVD) with a variety of doping densities chosen to broadly
modulate the transverse spin lifetime, T2*. The spin polarization is
characterized as a function of electrical excitation energy over a range of
temperatures. Despite weak spin-orbit interactions in GaN, a current-induced
spin polarization (CISP) is observed in the material at temperatures of up to
200 K.Comment: 16 pages, 3 figure
An investigation of the reaction of titanium with hydrogen Summary report
Hydrogen gas reaction with titanium and titanium alloys determined at low temperatures and pressure
From widespread Mississippian to localized Pennsylvanian extension in central Spitsbergen, Svalbard
In the Devonian–Carboniferous, a rapid succession of clustered extensional
and contractional tectonic events is thought to have affected sedimentary
rocks in central Spitsbergen, Svalbard. These events include Caledonian
post-orogenic extensional collapse associated with the formation of thick
Early–Middle Devonian basins, Late Devonian–Mississippian Ellesmerian
contraction, and Early–Middle Pennsylvanian rifting, which resulted in the
deposition of thick sedimentary units in Carboniferous basins like the
Billefjorden Trough. The clustering of these varied tectonic settings sometimes makes
it difficult to resolve the tectono-sedimentary history of
individual stratigraphic units. Notably, the context of deposition of
Mississippian clastic and coal-bearing sedimentary rocks of the Billefjorden
Group is still debated, especially in central Spitsbergen. We present field
evidence (e.g., growth strata and slickensides) from the northern part of the
Billefjorden Trough, in Odellfjellet, suggesting that tilted Mississippian
sedimentary strata of the Billefjorden Group deposited during active
(Late/latest?) Mississippian extension. WNW–ESE-striking basin-oblique
faults showing Mississippian growth strata systematically die out upwards
within Mississippian to lowermost Pennsylvanian strata, thus suggesting a
period of widespread WNW–ESE-directed extension in the Mississippian and an
episode of localized extension in Early–Middle Pennsylvanian times. In
addition, the presence of abundant basin-oblique faults in basement rocks
adjacent to the Billefjorden Trough suggests that the formation of
Mississippian normal faults was partly controlled by reactivation of
preexisting Neoproterozoic (Timanian?) basement-seated fault zones. We
propose that these preexisting faults reactivated as transverse or
accommodation cross faults in or near the crest of transverse folds
reflecting differential displacement along the Billefjorden Fault Zone. In
Cenozoic times, a few margin-oblique faults (e.g., the Overgangshytta fault)
may have mildly reactivated as oblique thrusts during
transpression–contraction, but shallow-dipping, bedding-parallel, duplex-shaped décollements in shales of the Billefjorden Group possibly
prevented substantial movement along these faults.</p
The Principles of Social Order. Selected Essays of Lon L. Fuller, edited With an introduction by Kenneth I. Winston
The electron spins of semiconductor defects can have complex interactions with their host, particularly in polar materials like SiC where electrical and mechanical variables are intertwined. By combining pulsed spin resonance with ab initio simulations, we show that spin-spin interactions in 4H-SiC neutral divacancies give rise to spin states with a strong Stark effect, sub-10(-6) strain sensitivity, and highly spin-dependent photoluminescence with intensity contrasts of 15%-36%. These results establish SiC color centers as compelling systems for sensing nanoscale electric and strain fields
Polytype control of spin qubits in silicon carbide
Crystal defects can confine isolated electronic spins and are promising
candidates for solid-state quantum information. Alongside research focusing on
nitrogen vacancy centers in diamond, an alternative strategy seeks to identify
new spin systems with an expanded set of technological capabilities, a
materials driven approach that could ultimately lead to "designer" spins with
tailored properties. Here, we show that the 4H, 6H and 3C polytypes of SiC all
host coherent and optically addressable defect spin states, including spins in
all three with room-temperature quantum coherence. The prevalence of this spin
coherence shows that crystal polymorphism can be a degree of freedom for
engineering spin qubits. Long spin coherence times allow us to use double
electron-electron resonance to measure magnetic dipole interactions between
spin ensembles in inequivalent lattice sites of the same crystal. Together with
the distinct optical and spin transition energies of such inequivalent spins,
these interactions provide a route to dipole-coupled networks of separately
addressable spins.Comment: 28 pages, 5 figures, and supplementary information and figure
A Search for Energy Minimized Sequences of Proteins
In this paper, we present numerical evidence that supports the notion of minimization in the sequence space of proteins for a target conformation. We use the conformations of the real proteins in the Protein Data Bank (PDB) and present computationally efficient methods to identify the sequences with minimum energy. We use edge-weighted connectivity graph for ranking the residue sites with reduced amino acid alphabet and then use continuous optimization to obtain the energy-minimizing sequences. Our methods enable the computation of a lower bound as well as a tight upper bound for the energy of a given conformation. We validate our results by using three different inter-residue energy matrices for five proteins from protein data bank (PDB), and by comparing our energy-minimizing sequences with 80 million diverse sequences that are generated based on different considerations in each case. When we submitted some of our chosen energy-minimizing sequences to Basic Local Alignment Search Tool (BLAST), we obtained some sequences from non-redundant protein sequence database that are similar to ours with an E-value of the order of 10-7. In summary, we conclude that proteins show a trend towards minimizing energy in the sequence space but do not seem to adopt the global energy-minimizing sequence. The reason for this could be either that the existing energy matrices are not able to accurately represent the inter-residue interactions in the context of the protein environment or that Nature does not push the optimization in the sequence space, once it is able to perform the function
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