4,834 research outputs found
Electrical activation and electron spin coherence of ultra low dose antimony implants in silicon
We implanted ultra low doses (2x10^11 cm-2) of 121Sb ions into isotopically
enriched 28Si and find high degrees of electrical activation and low levels of
dopant diffusion after rapid thermal annealing. Pulsed Electron Spin Resonance
shows that spin echo decay is sensitive to the dopant depths, and the interface
quality. At 5.2 K, a spin decoherence time, T2, of 0.3 ms is found for profiles
peaking 50 nm below a Si/SiO2 interface, increasing to 0.75 ms when the surface
is passivated with hydrogen. These measurements provide benchmark data for the
development of devices in which quantum information is encoded in donor
electron spins
Experimental Observation of a Minority Electron Mobility Enhancement in degenerately doped p-Type GaAs
The variation of minority electron mobility with doping density in p+-GaAs has been measured with the zero-field time-of-flight technique. The results from a series of nine GaAs films doped between 1 X lOI and 8 X 10â cmm3 show the mobility decreasing from 1950 cm2 V-â s-l at 1 X 10â cmm3 to 1370 cm2 V-l s-l at 9X 10â cmB3. For the doping range 9 x 1018-8x 1019 cme3, the decreasing trend in mobility is reversed. The measured mobility of 3710 cm2 V-â s-l at 8 X 10â cmp3 is about three times higher than the measured value at 9 X 1018 cmm3. These results confirm and extend recent transistor-based measurements and are in accord with recent theoretical predictions that attribute the increase in minority electron mobility in p+-GaAs to reductions in plasmon and carrier-carrier scattering at high hole densities
Comparative study of minority electron properties in p+-GaAs doped with beryllium and carbon
Minority electron properties in p+âGaAs doped with beryllium (Be) and with carbon (C) are reported. Measurements of essentially identical responses for structures differing only in dopant element demonstrate that the diffusivity (Dn) and the diffusion lengths (Ln) are the same in p+âGaAs doped to âŒ1019 cmâ3 with Beâ and Câdopants. Zeroâfield timeâofâflight analysis yields Dn=35 cm2/s and internal quantum efficiency analysis yields Ln=2.4 ÎŒm, which implies a lifetime that is approximately at the estimated radiative limit. In addition, the majority Hall mobility was also found to be identical for the Beâ and Câdoped material
Narrow optical linewidths in erbium implanted in TiO
Atomic and atom-like defects in the solid-state are widely explored for
quantum computers, networks and sensors. Rare earth ions are an attractive
class of atomic defects that feature narrow spin and optical transitions that
are isolated from the host crystal, allowing incorporation into a wide range of
materials. However, the realization of long electronic spin coherence times is
hampered by magnetic noise from abundant nuclear spins in the most widely
studied host crystals. Here, we demonstrate that Er ions can be
introduced via ion implantation into TiO, a host crystal that has not been
studied extensively for rare earth ions and has a low natural abundance of
nuclear spins. We observe efficient incorporation of the implanted Er
into the Ti site (40% yield), and measure narrow inhomogeneous spin and
optical linewidths (20 and 460 MHz, respectively) that are comparable to
bulk-doped crystalline hosts for Er. This work demonstrates that ion
implantation is a viable path to studying rare earth ions in new hosts, and is
a significant step towards realizing individually addressed rare earth ions
with long spin coherence times for quantum technologies
Thixotropy in macroscopic suspensions of spheres
An experimental study of the viscosity of a macroscopic suspension, i.e. a
suspension for which Brownian motion can be neglected, under steady shear is
presented. The suspension is prepared with a high packing fraction and is
density-matched in a Newtonian carrier fluid. The viscosity of the suspension
depends on the shear rate and the time of shearing. It is shown for the first
time that a macroscopic suspension shows thixotropic viscosity, i.e.
shear-thinning with a long relaxation time as a unique function of shear. The
relaxation times show a systematic decrease with increasing shear rate. These
relaxation times are larger when decreasing the shear rates, compared to those
observed after increasing the shear. The time scales involved are about 10000
times larger than the viscous time scale and about 1000 times smaller than the
thermodynamic time scale. The structure of the suspension at the outer cylinder
of a viscometer is monitored with a camera, showing the formation of a
hexagonal structure. The temporal decrease of the viscosity under shear
coincides with the formation of this hexagonal pattern
Metal-insulator transition in a doubly orbitally degenerate model with correlated hopping
In the present paper we propose a doubly orbitally degenerate narrow-band
model with correlated hopping. The peculiarity of the model is taking into
account the matrix element of electron-electron interaction which describes
intersite hoppings of electrons. In particular, this leads to the concentration
dependence of the effective hopping integral. The cases of the strong and weak
Hund's coupling are considered. By means of a generalized mean-field
approximation the single-particle Green function and quasiparticle energy
spectrum are calculated. Metal-insulator transition is studied in the model at
different integer values of the electron concentration. With the help of the
obtained energy spectrum we find energy gap width and criteria of
metal-insulator transition.Comment: minor revisions, published in Phys. Rev.
Regulating CCTV? : We can't solve problems by using the same kind of thinking we used when we created them
Peer reviewedPostprin
Hepatitis C virus infection protein network
A proteome-wide mapping of interactions between hepatitis C virus (HCV) and human proteins was performed to provide a comprehensive view of the cellular infection. A total of 314 proteinâprotein interactions between HCV and human proteins was identified by yeast two-hybrid and 170 by literature mining. Integration of this data set into a reconstructed human interactome showed that cellular proteins interacting with HCV are enriched in highly central and interconnected proteins. A global analysis on the basis of functional annotation highlighted the enrichment of cellular pathways targeted by HCV. A network of proteins associated with frequent clinical disorders of chronically infected patients was constructed by connecting the insulin, Jak/STAT and TGFÎČ pathways with cellular proteins targeted by HCV. CORE protein appeared as a major perturbator of this network. Focal adhesion was identified as a new function affected by HCV, mainly by NS3 and NS5A proteins
First Steps in Eukaryogenesis: Physical phenomena in the origin and evolution of chromosome structure
Our present understanding of the origin and evolution of chromosomes differs considerably from current understanding of the origin and evolution of the cell itself. Chromosome origins have been less prominent in research, as the emphasis has not shifted so far appreciably from the phenomenon of primeval nucleic acid encapsulation to that of the origin of gene organization, expression, and regulation. In this work we discuss some reasons why preliminary steps in this direction are being taken. We have been led to examine properties that have contributed to raise the ancestral prokaryotic programmes to a level where we can appreciate in eukaryotes a clear departure from earlier themes in the evolution of the cell from the last common ancestor. We shift our point of view from the evolution of cell morphology to the point of view of the genes. In particular, we focus attention on possible physical bases for the way transmission of information has evolved in eukaryotes, namely, the inactivation of whole chromosomes. The special case of the inactivation of the X chromosome in mammals is discussed, paying particular attention to the physical process of the spread of X inactivation in monotremes (platypus and echidna). When experimental data is unavailable some theoretical analysis is possible based on the idea that in certain cases collective phenomena in genetics, rather than chemical detail, are better correlates of complex chemical processes
Measurement of the rate of nu_e + d --> p + p + e^- interactions produced by 8B solar neutrinos at the Sudbury Neutrino Observatory
Solar neutrinos from the decay of B have been detected at the Sudbury
Neutrino Observatory (SNO) via the charged current (CC) reaction on deuterium
and by the elastic scattering (ES) of electrons. The CC reaction is sensitive
exclusively to nu_e's, while the ES reaction also has a small sensitivity to
nu_mu's and nu_tau's. The flux of nu_e's from ^8B decay measured by the CC
reaction rate is
\phi^CC(nu_e) = 1.75 +/- 0.07 (stat)+0.12/-0.11 (sys.) +/- 0.05(theor) x 10^6
/cm^2 s.
Assuming no flavor transformation, the flux inferred from the ES reaction
rate is
\phi^ES(nu_x) = 2.39+/-0.34 (stat.)+0.16}/-0.14 (sys) x 10^6 /cm^2 s.
Comparison of \phi^CC(nu_e) to the Super-Kamiokande Collaboration's precision
value of \phi^ES(\nu_x) yields a 3.3 sigma difference, providing evidence that
there is a non-electron flavor active neutrino component in the solar flux. The
total flux of active ^8B neutrinos is thus determined to be 5.44 +/-0.99 x
10^6/cm^2 s, in close agreement with the predictions of solar models.Comment: 6 pages (LaTex), 3 figures, submitted to Phys. Rev. Letter
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