1,468 research outputs found
Semi-classical Green kernel asymptotics for the Dirac operator
We consider a semi-classical Dirac operator in arbitrary spatial dimensions
with a smooth potential whose partial derivatives of any order are bounded by
suitable constants. We prove that the distribution kernel of the inverse
operator evaluated at two distinct points fulfilling a certain hypothesis can
be represented as the product of an exponentially decaying factor involving an
associated Agmon distance and some amplitude admitting a complete asymptotic
expansion in powers of the semi-classical parameter. Moreover, we find an
explicit formula for the leading term in that expansion.Comment: 46 page
Physical Study by Surface Characterizations of Sarin Sensor on the Basis of Chemically Functionalized Silicon Nanoribbon Field Effect Transistor
Surface characterizations of an organophosphorus (OP) gas detector based on
chemically functionalized silicon nanoribbon field-effect transistor (SiNR-FET)
were performed by Kelvin Probe Force Microscopy (KPFM) and ToF-SIMS, and
correlated with changes in the current-voltage characteristics of the devices.
KPFM measurements on FETs allow (i) to investigate the contact potential
difference (CPD) distribution of the polarized device as function of the gate
voltage and the exposure to OP traces and, (ii) to analyze the CPD hysteresis
associated to the presence of mobile ions on the surface. The CPD measured by
KPFM on the silicon nanoribbon was corrected due to side capacitance effects in
order to determine the real quantitative surface potential. Comparison with
macroscopic Kelvin probe (KP) experiments on larger surfaces was carried out.
These two approaches were quantitatively consistent. An important increase of
the CPD values (between + 399 mV and + 302 mV) was observed after the OP sensor
grafting, corresponding to a decrease of the work function, and a weaker
variation after exposure to OP (between - 14 mV and - 61 mV) was measured.
Molecular imaging by ToF-SIMS revealed OP presence after SiNR-FET exposure. The
OP molecules were essentially localized on the Si-NR confirming effectiveness
and selectivity of the OP sensor. A prototype was exposed to Sarin vapors and
succeeded in the detection of low vapor concentrations (40 ppm).Comment: Paper and supporting information, J. Phys. Chem. C, 201
Experimental Verification of 3D Plasmonic Cloaking in Free-Space
We report the experimental verification of metamaterial cloaking for a 3D
object in free space. We apply the plasmonic cloaking technique, based on
scattering cancellation, to suppress microwave scattering from a finite-length
dielectric cylinder. We verify that scattering suppression is obtained all
around the object in the near- and far-field and for different incidence
angles, validating our measurements with analytical results and full-wave
simulations. Our near-field and far-field measurements confirm that realistic
and robust plasmonic metamaterial cloaks may be realized for elongated 3D
objects with moderate transverse cross-section at microwave frequencies.Comment: 12 pages, 8 figures, published in NJ
The Origin of the Designability of Protein Structures
We examined what determines the designability of 2-letter codes (H and P)
lattice proteins from three points of view. First, whether the native structure
is searched within all possible structures or within maximally compact
structures. Second, whether the structure of the used lattice is bipartite or
not. Third, the effect of the length of the chain, namely, the number of
monomers on the chain. We found that the bipartiteness of the lattice structure
is not a main factor which determines the designability. Our results suggest
that highly designable structures will be found when the length of the chain is
sufficiently long to make the hydrophobic core consisting of enough number of
monomers.Comment: 17 pages, 2 figure
Bond-randomness-induced Neel order in weakly coupled antiferromagnetic spin chains
Quasi-one-dimensional antiferromagnetic (AF) quantum spin systems show a wide
range of interesting phenomena such as the spin-Peierls transition and disorder
driven long range ordering. While there is no magnetic long range order in
strictly one-dimensional systems, in real systems some amount of interchain
coupling is always present and AF long range order may appear below a Neel
ordering temperature T_N. We study the effect of bond randomness on Neel
ordering in weakly coupled random AF S=1/2 chains both with and without
dimerization (or spin-Peierls order). We use the real space renormalization
group method to tackle the intrachain couplings, and a mean-field approximation
to treat the interchain coupling. We show that in the non-dimerized chain,
disorder (represented by bond randomness) enhances the Neel order parameter; in
the dimerized chain which shows no magnetic ordering in the weak interchain
coupling limit without randomness, disorder can actually lead to long range
order. Thus disorder is shown to lead to, or enhance the tendency toward long
range order, providing another example of the order-by-disorder phenomenon. We
make a qualitative comparison of our results with the observed phenomenon of
doping induced long range ordering in quasi-one-dimensional spin systems such
as CuGeO_3.Comment: 8 pages, 4 figure
Cassini observations of ion and electron beams at Saturn and their relationship to infrared auroral arcs
We present Cassini Visual and Infrared Mapping Spectrometer observations of infrared auroral emissions from the noon sector of Saturn's ionosphere revealing multiple intense auroral arcs separated by dark regions poleward of the main oval. The arcs are interpreted as the ionospheric signatures of bursts of reconnection occurring at the dayside magnetopause. The auroral arcs were associated with upward field-aligned currents, the magnetic signatures of which were detected by Cassini at high planetary latitudes. Magnetic field and particle observations in the adjacent downward current regions showed upward bursts of 100–360 keV light ions in addition to energetic (hundreds of keV) electrons, which may have been scattered from upward accelerated beams carrying the downward currents. Broadband, upward propagating whistler waves were detected simultaneously with the ion beams. The acceleration of the light ions from low altitudes is attributed to wave-particle interactions in the downward current regions. Energetic (600 keV) oxygen ions were also detected, suggesting the presence of ambient oxygen at altitudes within the acceleration region. These simultaneous in situ and remote observations reveal the highly energetic magnetospheric dynamics driving some of Saturn's unusual auroral features. This is the first in situ identification of transient reconnection events at regions magnetically conjugate to Saturn's magnetopause
Random Antiferromagnetic Spin-1/2 Chains with Competing Interactions
We study disordered antiferromagnetic spin-1/2 chains with nearest- and
further-neighbor interactions using the real-space renormalization-group
method. We find that the system supports two different phases, depending on the
ratio of the strength between nearest-neighbor and further-neighbor
interactions as well the bond randomness strength. For weak further neighbor
coupling the system is in the familiar random singlet phase, while stronger
further neighbor coupling drives the system to a large spin phase similar to
that found in the study of random antiferromagnetic-ferromagnetic spin chains.
The appearance of the large spin phase in the absence of ferromagnetic coupling
is due to the frustration introduced by further neighboring couplings, and is
unique to the disordered chains.Comment: 11 pages, 7 figure
Random interactions and spin-glass thermodynamic transition in the hole-doped Haldane system YCaBaNiO
Magnetization, DC and AC bulk susceptibility of the =1 Haldane chain
system doped with electronic holes, YCaBaNiO
(0x0.20), have been measured and analyzed. The most striking
results are (i) a sub-Curie power law behavior of the linear susceptibility,
, for temperature lower than the Haldane gap
of the undoped compound (x=0) (ii) the existence of a spin-glass thermodynamic
transition at = 2-3 K. These findings are consistent with (i) random
couplings within the chains between the spin degrees of freedom induced by hole
doping, (ii) the existence of ferromagnetic bonds that induce magnetic
frustration when interchain interactions come into play at low temperature.Comment: 4 pages, 4 figures, to appear in Phys. Rev.
Recently Integrated Alu Elements In Capuchin Monkeys: A Resource For Cebus/Sapajus Genomics
Capuchins are platyrrhines (monkeys found in the Americas) within the Cebidae family. For most of their taxonomic history, the two main morphological types of capuchins, gracile (untufted) and robust (tufted), were assigned to a single genus, Cebus. Further, all tufted capuchins were assigned to a single species, Cebus apella, despite broad geographic ranges spanning Central and northern South America. In 2012, tufted capuchins were assigned to their genus, Sapajus, with eight currently recognized species and five Cebus species, although these numbers are still under debate. Alu retrotransposons are a class of mobile element insertion (MEI) widely used to study primate phylogenetics. However, Alu elements have rarely been used to study capuchins. Recent genome-level assemblies for capuchins (Cebus imitator; [Cebus_imitator_1.0] and Sapajus apella [GSC_monkey_1.0]) facilitated large scale ascertainment of young lineage-specific Alu insertions. Reported here are 1607 capuchin specific and 678 Sapajus specific Alu insertions along with candidate oligonucleotides for locus-specific PCR assays for many elements. PCR analyses identified 104 genus level and 51 species level Alu insertion polymorphisms. The Alu datasets reported in this study provide a valuable resource that will assist in the classification of archival samples lacking phenotypic data and for the study of capuchin phylogenetic relationships
COVID-19 outbreak at a reception centre for asylum seekers in Espoo, Finland
Publisher Copyright: © 2021Background shared accommodation may increase the risk of SARS-CoV-2 transmission. In April 2020, an increasing number of asylum seekers at a reception centre in Espoo, Finland presented with COVID-19 despite earlier implementation of preventive measures. We decided to screen the entire population of the centre for SARS-CoV-2. Methods we offered nasopharyngeal swab collection and SARS-CoV-2 real-time polymerase chain reaction (RT-PCR) analysis to the centre's clients. Symptoms were recorded at the time of diagnostic sample collection using electronic forms and followed up for two weeks through phone interviews and a review of medical records. Findings 260 clients were screened. Of them, 96 (37%) were found positive for SARS-CoV-2 and isolated. The high attack rate prompted the local public health authority to set the other clients in quarantine for 14 days to prevent further spread. Of the positive cases, 61 (64%) reported having had symptoms at the time of the screening or one week prior. Of the 35 initially asymptomatic individuals, 12 developed symptoms during follow-up, while 23 (or 18% of all screened SARS-CoV-2 positive clients) remained asymptomatic. No widespread transmission of COVID-19 was detected after the quarantine was lifted. Interpretation in this large COVID-19 outbreak, voluntary mass screening provided valuable information about its extent and helped guide the public health response. Comprehensive quarantine and isolation measures were likely instrumental in containing the outbreak. Funding Finnish Institution for Health and Welfare, Finnish Immigration Agency, City of EspooPeer reviewe
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