4,687 research outputs found
Critical assessment of two-qubit post-Markovian master equations
A post-Markovian master equation has been recently proposed as a tool to
describe the evolution of a system coupled to a memory-keeping environment [A.
Shabani and D. A. Lidar, Phys. Rev. A 71, 020101 (R) (2005)]. For a single
qubit affected by appropriately chosen environmental conditions, the
corresponding dynamics is always legitimate and physical. Here we extend such
situation to the case of two qubits, only one of which experiences the
environmental effects. We show how, despite the innocence of such an extension,
the introduction of the second qubit should be done cum grano salis to avoid
consequences such as the breaking of the positivity of the associated dynamical
map. This hints at the necessity of using care when adopting phenomenologically
derived models for evolutions occurring outside the Markovian framework.Comment: 7 pages, 1 figure, RevTeX4. Close to published versio
A Clinical and Epidemiological Investigation of the First Reported Human Infection With the Zoonotic Parasite Trypanosoma evansi in Southeast Asia
Background. Trypanosoma is a genus of unicellular parasitic flagellate protozoa. Trypanosoma brucei species and Trypanosoma cruzi are the major agents of human trypanosomiasis; other Trypanosoma species can cause human disease, but are rare. In March 2015, a 38-year-old woman presented to a healthcare facility in southern Vietnam with fever, headache, and arthralgia. Microscopic examination of blood revealed infection with Trypanosoma. Methods. Microscopic observation, polymerase chain reaction (PCR) amplification of blood samples, and serological testing were performed to identify the infecting species. The patient's blood was screened for the trypanocidal protein apolipoprotein L1 (APOL1), and a field investigation was performed to identify the zoonotic source. Results. PCR amplification and serological testing identified the infecting species as Trypanosoma evansi. Despite relapsing 6 weeks after completing amphotericin B therapy, the patient made a complete recovery after 5 weeks of suramin. The patient was found to have 2 wild-type APOL1 alleles and a normal serum APOL1 concentration. After responsive animal sampling in the presumed location of exposure, cattle and/or buffalo were determined to be the most likely source of the infection, with 14 of 30 (47%) animal blood samples testing PCR positive for T. evansi. Conclusions. We report the first laboratory-confirmed case of T. evansi in a previously healthy individual without APOL1 deficiency, potentially contracted via a wound while butchering raw beef, and successfully treated with suramin. A linked epidemiological investigation revealed widespread and previously unidentified burden of T. evansi in local cattle, highlighting the need for surveillance of this infection in animals and the possibility of further human cases
Quantum control and quantum speed limits in supersymmetric potentials
Supersymmetry allows one to build a hierarchy of Hamiltonians that share the same spectral properties and which are pairwise connected through common super-potentials. The iso-spectral properties of these Hamiltonians imply that the dynamics and therefore control of different eigenstates are connected through supersymmetric intertwining relations. In this work we explore how this enables one to study general dynamics, shortcuts to adiabaticity and quantum speed limits for distinct states of different supersymmetric partner potentials by using the infinite box as an example
Outflows from the high-mass protostars NGC 7538 IRS1/2 observed with bispectrum speckle interferometry -- Signatures of flow precession
NGC 7538 IRS1 is a high-mass (approx. 30 M_sun) protostar with a CO outflow,
an associated UCHII region, and a linear methanol maser structure, which might
trace a Keplerian-rotating circumstellar disk. The directions of the various
associated axes are misaligned with each other. We investigate the
near-infrared morphology of the source to clarify the relations among the
various axes. K'-band bispectrum speckle interferometry was performed at two
6-meter-class telescopes -- the BTA 6m telescope and the 6.5m MMT.
Complementary IRAC images from the Spitzer Space Telescope Archive were used to
relate the structures detected with the outflow at larger scales. High-dynamic
range images show fan-shaped outflow structure in which we detect 18 stars and
several blobs of diffuse emission. We interpret the misalignment of various
outflow axes in the context of a disk precession model, including numerical
hydrodynamic simulations of the molecular emission. The precession period is
approx. 280 years and its half-opening angle is 40 degrees. A possible
triggering mechanism is non-coplanar tidal interaction of an (undiscovered)
close companion with the circumbinary protostellar disk. Our observations
resolve the nearby massive protostar NGC 7538 IRS2 as a close binary with
separation of 195 mas. We find indications for shock interaction between the
outflow activities in IRS1 and IRS2. Indications of outflow precession have
been discovered to date in a number of massive protostars, all with large
precession angles 20--45 degrees. This might explain the difference between the
outflow widths in low- and high-mass stars and add support to a common
collimation mechanism.Comment: 20 pages; 8 figures; Accepted by A&A on April 10, 2006; Image quality
reduced due to astro-ph file size limitations; Please download a version with
high-quality images from
http://www.mpifr-bonn.mpg.de/staff/tpreibis/ngc7538.pd
Analytic Solution for the Critical State in Superconducting Elliptic Films
A thin superconductor platelet with elliptic shape in a perpendicular
magnetic field is considered. Using a method originally applied to circular
disks, we obtain an approximate analytic solution for the two-dimensional
critical state of this ellipse. In the limits of the circular disk and the long
strip this solution is exact, i.e. the current density is constant in the
region penetrated by flux. For ellipses with arbitrary axis ratio the obtained
current density is constant to typically 0.001, and the magnetic moment
deviates by less than 0.001 from the exact value. This analytic solution is
thus very accurate. In increasing applied magnetic field, the penetrating flux
fronts are approximately concentric ellipses whose axis ratio b/a < 1 decreases
and shrinks to zero when the flux front reaches the center, the long axis
staying finite in the fully penetrated state. Analytic expressions for these
axes, the sheet current, the magnetic moment, and the perpendicular magnetic
field are presented and discussed. This solution applies also to
superconductors with anisotropic critical current if the anisotropy has a
particular, rather realistic form.Comment: Revtex file and 13 postscript figures, gives 10 pages of text with
figures built i
The high-mass disk candidates NGC7538IRS1 and NGC7538S
Context: The nature of embedded accretion disks around forming high-mass
stars is one of the missing puzzle pieces for a general understanding of the
formation of the most massive and luminous stars. Methods: Using the Plateau de
Bure Interferometer at 1.36mm wavelengths in its most extended configuration we
probe the dust and gas emission at ~0.3",corresponding to linear resolution
elements of ~800AU. Results: NGC7538IRS1 remains a single compact and massive
gas core with extraordinarily high column densities, corresponding to visual
extinctions on the order of 10^5mag, and average densities within the central
2000AU of ~2.1x10^9cm^-3 that have not been measured before. We identify a
velocity gradient across in northeast-southwest direction that is consistent
with the mid-infrared emission, but we do not find a gradient that corresponds
to the proposed CH3OH maser disk. The spectral line data toward NGC7538IRS1
reveal strong blue- and red-shifted absorption toward the mm continuum peak
position. The red-shifted absorption allows us to estimate high infall rates on
the order of 10^-2 Msun/yr. Although we cannot prove that the gas will be
accreted in the end, the data are consistent with ongoing star formation
activity in a scaled-up low-mass star formation scenario. Compared to that,
NGC7538S fragments in a hierarchical fashion into several sub-sources. While
the kinematics of the main mm peak are dominated by the accompanying jet, we
find rotational signatures from a secondary peak. Furthermore, strong spectral
line differences exist between the sub-sources which is indicative of different
evolutionary stages within the same large-scale gas clump.Comment: 15 pages, 12 figures, accepted for A&
Critical State in Thin Anisotropic Superconductors of Arbitrary Shape
A thin flat superconductor of arbitrary shape and with arbitrary in-plane and
out-of-plane anisotropy of flux-line pinning is considered, in an external
magnetic field normal to its plane.
It is shown that the general three-dimensional critical state problem for
this superconductor reduces to the two-dimensional problem of an infinitely
thin sample of the same shape but with a modified induction dependence of the
critical sheet current. The methods of solving the latter problem are well
known. This finding thus enables one to study the critical states in realistic
samples of high-Tc superconductors with various types of anisotropic flux-line
pinning. As examples, we investigate the critical states of long strips and
rectangular platelets of high-Tc superconductors with pinning either by the
ab-planes or by extended defects aligned with the c-axis.Comment: 13 pages including 13 figure files in the tex
DNA end resection by Dna2–Sgs1–RPA and its stimulation by Top3–Rmi1 and Mre11–Rad50–Xrs2
The repair of DNA double-strand breaks (DSBs) by homologous recombination requires processing of broken ends. For repair to start, the DSB must first be resected to generate a 3′-single-stranded DNA (ssDNA) overhang, which becomes a substrate for the DNA strand exchange protein, Rad51 (ref. 1). Genetic studies have implicated a multitude of proteins in the process, including helicases, nucleases and topoisomerases. Here we biochemically reconstitute elements of the resection process and reveal that it requires the nuclease Dna2, the RecQ-family helicase Sgs1 and the ssDNA-binding protein replication protein-A (RPA). We establish that Dna2, Sgs1 and RPA constitute a minimal protein complex capable of DNA resection in vitro. Sgs1 helicase unwinds the DNA to produce an intermediate that is digested by Dna2, and RPA stimulates DNA unwinding by Sgs1 in a species-specific manner. Interestingly, RPA is also required both to direct Dna2 nucleolytic activity to the 5′-terminated strand of the DNA break and to inhibit 3′ to 5′ degradation by Dna2, actions that generate and protect the 3′-ssDNA overhang, respectively. In addition to this core machinery, we establish that both the topoisomerase 3 (Top3) and Rmi1 complex and the Mre11–Rad50–Xrs2 complex (MRX) have important roles as stimulatory components. Stimulation of end resection by the Top3–Rmi1 heterodimer and the MRX proteins is by complex formation with Sgs1 (refs 5, 6), which unexpectedly stimulates DNA unwinding. We suggest that Top3–Rmi1 and MRX are important for recruitment of the Sgs1–Dna2 complex to DSBs. Our experiments provide a mechanistic framework for understanding the initial steps of recombinational DNA repair in eukaryotes
The antimicrobial resistance patterns and associated determinants in Streptococcus suis isolated from humans in southern Vietnam, 1997-2008
<p>Abstract</p> <p>Background</p> <p><it>Streptococcus suis </it>is an emerging zoonotic pathogen and is the leading cause of bacterial meningitis in adults in Vietnam. Systematic data on the antimicrobial susceptibility profiles of <it>S. suis </it>strains isolated from human cases are lacking. We studied antimicrobial resistance and associated resistance determinants in <it>S. suis </it>isolated from patients with meningitis in southern Vietnam.</p> <p>Methods</p> <p><it>S. suis </it>strains isolated between 1997 and 2008 were investigated for their susceptibility to six antimicrobial agents. Strains were screened for the presence and expression of tetracycline and erythromycin resistance determinants and the association of <it>tet</it>(M) genes with <it>Tn</it>916- like transposons. The localization of tetracycline resistance gene <it>tet</it>(L) was determined by pulse field gel electrophoresis and Southern blotting.</p> <p>Results</p> <p>We observed a significant increase in resistance to tetracycline and chloramphenicol, which was concurrent with an increase in multi-drug resistance. In tetracycline resistance strains, we identified <it>tet</it>(M), <it>tet</it>(O), <it>tet</it>(W) and <it>tet</it>(L) and confirmed their expression. All <it>tet</it>(M) genes were associated with a <it>Tn</it>916-like transposon. The co-expression of <it>tet</it>(L) and other tetracycline resistance gene(s) encoding for ribosomal protection protein(s) was only detected in strains with a minimum inhibitory concentration (MIC) of tetracycline of ≥ 64 mg/L</p> <p>Conclusions</p> <p>We demonstrated that multi-drug resistance in <it>S. suis </it>causing disease in humans in southern Vietnam has increased over the 11-year period studied. We report the presence and expression of <it>tet</it>(L) in <it>S. suis </it>strains and our data suggest that co-expression of multiple genes encoding distinct mechanism is required for an MIC ≥ 64 mg/L to tetracycline.</p
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