3,625 research outputs found
ASTROD, ASTROD I and their gravitational-wave sensitivities
ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) is a
mission concept with three spacecraft -- one near L1/L2 point, one with an
inner solar orbit and one with an outer solar orbit, ranging coherently with
one another using lasers to test relativistic gravity, to measure the solar
system and to detect gravitational waves. ASTROD I with one spacecraft ranging
optically with ground stations is the first step toward the ASTROD mission. In
this paper, we present the ASTROD I payload and accelerometer requirements,
discuss the gravitational-wave sensitivities for ASTROD and ASTROD I, and
compare them with LISA and radio-wave PDoppler-tracking of spacecraft.Comment: presented to the 5th Edoardo Amaldi Conference (July 6-11, 2003) and
submitted to Classical and Quantum Gravit
Strong quantum fluctuation of vortices in the new superconductor
By using transport and magnetic measurement, the upper critical field
and the irreversibility line has been determined. A
big separation between and has been found showing the
existence of a quantum vortex liquid state induced by quantum fluctuation of
vortices in the new superconductor . Further investigation on the
magnetic relaxation shows that both the quantum tunneling and the thermally
activated flux creep weakly depends on temperature. But when the melting field
is approached, a drastic rising of the relaxation rate is observed.
This may imply that the melting of the vortex matter at a finite temperature is
also induced by the quantum fluctuation of vortices.Comment: 4 pages, 4 figure
Superconductivity in a layered cobalt oxyhydrate NaCoO1.3HO
We report the electrical, magnetic and thermal measurements on a layered
cobalt oxyhydrate NaCoO1.3HO. Bulk superconductivity
at 4.3 K has been confirmed, however, the measured superconducting fraction is
relatively low probably due to the sample's intrinsic two-dimensional
characteristic. The compound exhibits weak-coupled and extreme type-II
superconductivity with the average energy gap and the
Ginzburg-Landau parameter of 0.50 meV and 140,
respectively. The normalized electronic specific heat data in the
superconducting state well fit the dependence, suggesting point nodes
for the superconducting gap structure.Comment: 4 pages, 3 figure
Compulsory reduced working time in Belarus: Incidence, operation and consequences
This article examines compulsory reduced working time (CRWT) in five Belarusian factories, to assess its impact on employment relationships and evaluate arguments about ‘Soviet legacies’ and labour ‘patience’. Local use of CRWT increased between 2001 and 2012, and took a form more inimical to worker interests, thereby differing from official macro statistics. Managers expressed discontent at being pushed by state policy to use CRWT, but used it as a disciplinary tool. Workers perceived worsening work relationships and threats of collective response were in evidence. Arguments about ‘Soviet legacies’ and labour’s ‘patience’ therefore currently appear inappropriate
Laser-induced etching of few-layer graphene synthesized by Rapid-Chemical Vapour Deposition on Cu thin films
The outstanding electrical and mechanical properties of graphene make it very
attractive for several applications, Nanoelectronics above all. However a
reproducible and non destructive way to produce high quality, large-scale area,
single layer graphene sheets is still lacking. Chemical Vapour Deposition of
graphene on Cu catalytic thin films represents a promising method to reach this
goal, because of the low temperatures (T < 900 Celsius degrees) involved during
the process and of the theoretically expected monolayer self-limiting growth.
On the contrary such self-limiting growth is not commonly observed in
experiments, thus making the development of techniques allowing for a better
control of graphene growth highly desirable. Here we report about the local
ablation effect, arising in Raman analysis, due to the heat transfer induced by
the laser incident beam onto the graphene sample.Comment: v1:9 pages, 8 figures, submitted to SpringerPlus; v2: 11 pages,
PDFLaTeX, 9 figures, revised peer-reviewed version resubmitted to
SpringerPlus; 1 figure added, figure 1 and 4 replaced,typos corrected,
"Results and discussion" section significantly extended to better explain
etching mechanism and features of Raman spectra, references adde
Interpreting Attoclock Measurements of Tunnelling Times
Resolving in time the dynamics of light absorption by atoms and molecules,
and the electronic rearrangement this induces, is among the most challenging
goals of attosecond spectroscopy. The attoclock is an elegant approach to this
problem, which encodes ionization times in the strong-field regime. However,
the accurate reconstruction of these times from experimental data presents a
formidable theoretical challenge. Here, we solve this problem by combining
analytical theory with ab-initio numerical simulations. We apply our theory to
numerical attoclock experiments on the hydrogen atom to extract ionization time
delays and analyse their nature. Strong field ionization is often viewed as
optical tunnelling through the barrier created by the field and the core
potential. We show that, in the hydrogen atom, optical tunnelling is
instantaneous. By calibrating the attoclock using the hydrogen atom, our method
opens the way to identify possible delays associated with multielectron
dynamics during strong-field ionization.Comment: 33 pages, 10 figures, 3 appendixe
Re-infection with a different SARS-CoV-2 clade and prolonged viral shedding in a hematopoietic stem cell transplantation patient
Immunocompromised patients who have a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection pose many clinical and public health challenges. We describe the case of a hematopoietic stem cell transplantation patient with lymphoma who had a protracted illness requiring three consecutive hospital admissions. Whole genome sequencing confirmed two different SARS-CoV-2 clades. Clinical management issues and the unanswered questions arising from this case are discussed
Astrodynamical Space Test of Relativity using Optical Devices I (ASTROD I) - A class-M fundamental physics mission proposal for Cosmic Vision 2015-2025: 2010 Update
This paper on ASTROD I is based on our 2010 proposal submitted for the ESA
call for class-M mission proposals, and is a sequel and an update to our
previous paper [Experimental Astronomy 23 (2009) 491-527; designated as Paper
I] which was based on our last proposal submitted for the 2007 ESA call. In
this paper, we present our orbit selection with one Venus swing-by together
with orbit simulation. In Paper I, our orbit choice is with two Venus
swing-bys. The present choice takes shorter time (about 250 days) to reach the
opposite side of the Sun. We also present a preliminary design of the optical
bench, and elaborate on the solar physics goals with the radiation monitor
payload. We discuss telescope size, trade-offs of drag-free sensitivities,
thermal issues and present an outlook. ASTROD I is a planned interplanetary
space mission with multiple goals. The primary aims are: to test General
Relativity with an improvement in sensitivity of over 3 orders of magnitude,
improving our understanding of gravity and aiding the development of a new
quantum gravity theory; to measure key solar system parameters with increased
accuracy, advancing solar physics and our knowledge of the solar system; and to
measure the time rate of change of the gravitational constant with an order of
magnitude improvement and the anomalous Pioneer acceleration, thereby probing
dark matter and dark energy gravitationally. It is envisaged as the first in a
series of ASTROD missions. ASTROD I will consist of one spacecraft carrying a
telescope, four lasers, two event timers and a clock. Two-way, two-wavelength
laser pulse ranging will be used between the spacecraft in a solar orbit and
deep space laser stations on Earth, to achieve the ASTROD I goals.Comment: 15 pages, 11 figures, 1 table, based on our 2010 proposal submitted
for the ESA call for class-M mission proposals, a sequel and an update to
previous paper [Experimental Astronomy 23 (2009) 491-527] which was based on
our last proposal submitted for the 2007 ESA call, submitted to Experimental
Astronom
Phase transitions in contagion processes mediated by recurrent mobility patterns
Human mobility and activity patterns mediate contagion on many levels,
including the spatial spread of infectious diseases, diffusion of rumors, and
emergence of consensus. These patterns however are often dominated by specific
locations and recurrent flows and poorly modeled by the random diffusive
dynamics generally used to study them. Here we develop a theoretical framework
to analyze contagion within a network of locations where individuals recall
their geographic origins. We find a phase transition between a regime in which
the contagion affects a large fraction of the system and one in which only a
small fraction is affected. This transition cannot be uncovered by continuous
deterministic models due to the stochastic features of the contagion process
and defines an invasion threshold that depends on mobility parameters,
providing guidance for controlling contagion spread by constraining mobility
processes. We recover the threshold behavior by analyzing diffusion processes
mediated by real human commuting data.Comment: 20 pages of Main Text including 4 figures, 7 pages of Supplementary
Information; Nature Physics (2011
Droplet-like Fermi surfaces in the anti-ferromagnetic phase of EuFeAs, an Fe-pnictide superconductor parent compound
Using angle resolved photoemission it is shown that the low lying electronic
states of the iron pnictide parent compound EuFeAs are strongly
modified in the magnetically ordered, low temperature, orthorhombic state
compared to the tetragonal, paramagnetic case above the spin density wave
transition temperature. Back-folded bands, reflected in the orthorhombic/
anti-ferromagnetic Brillouin zone boundary hybridize strongly with the
non-folded states, leading to the opening of energy gaps. As a direct
consequence, the large Fermi surfaces of the tetragonal phase fragment, the low
temperature Fermi surface being comprised of small droplets, built up of
electron and hole-like sections. These high resolution ARPES data are therefore
in keeping with quantum oscillation and optical data from other undoped
pnictide parent compounds.Comment: 4 figures, 6 page
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