6,172 research outputs found
Comment on "Layering transition in confined molecular thin films: Nucleation and growth"
When fluid is confined between two molecularly smooth surfaces to a few
molecular diameters, it shows a large enhancement of its viscosity. From
experiments it seems clear that the fluid is squeezed out layer by layer. A
simple solution of the Stokes equation for quasi-two-dimensional confined flow,
with the assmption of layer-by-layer flow is found. The results presented here
correct those in Phys. Rev. B, 50, 5590 (1994), and show that both the
kinematic viscosity of the confined fluid and the coefficient of surface drag
can be obtained from the time dependence of the area squeezed out. Fitting our
solution to the available experimental data gives the value of viscosity which
is ~7 orders of magnitude higher than that in the bulk.Comment: 4 pages, 2 figure
Spin and the Coulomb Gap in the Half-Filled Lowest Landau Level
The Coulomb gap observed in tunneling between parallel two-dimensional
electron systems, each at half filling of the lowest Landau level, is found to
depend sensitively on the presence of an in-plane magnetic field. Especially at
low electron density, the width of the Coulomb gap at first increases sharply
with in-plane field, but then abruptly levels off. This behavior appears to
coincide with the known transition from partial to complete spin polarization
of the half-filled lowest Landau level. The tunneling gap therefore opens a new
window onto the spin configuration of two-dimensional electron systems at high
magnetic field.Comment: 6 pages, 4 postscript figures. Minor changes. To appear in Physical
Review
Knowledge Rich Natural Language Queries over Structured Biological Databases
Increasingly, keyword, natural language and NoSQL queries are being used for
information retrieval from traditional as well as non-traditional databases
such as web, document, image, GIS, legal, and health databases. While their
popularity are undeniable for obvious reasons, their engineering is far from
simple. In most part, semantics and intent preserving mapping of a well
understood natural language query expressed over a structured database schema
to a structured query language is still a difficult task, and research to tame
the complexity is intense. In this paper, we propose a multi-level
knowledge-based middleware to facilitate such mappings that separate the
conceptual level from the physical level. We augment these multi-level
abstractions with a concept reasoner and a query strategy engine to dynamically
link arbitrary natural language querying to well defined structured queries. We
demonstrate the feasibility of our approach by presenting a Datalog based
prototype system, called BioSmart, that can compute responses to arbitrary
natural language queries over arbitrary databases once a syntactic
classification of the natural language query is made
Competition and coexistence of antiferromagnetism and superconductivity in underdoped Ba(Fe0.953Co0.047)2As2
Neutron and x-ray diffraction studies show that the simultaneous first-order
transition to an orthorhombic and antiferromagnetic (AFM) ordered state in
BaFe2As2 splits into two transitions with Co doping. For
Ba(Fe0.953Co0.047)2As2, a tetragonal-orthorhombic transition occurs at TS = 60
K, followed by a second-order transition to AFM order at TN = 47 K.
Superconductivity (SC) occurs in the orthorhombic state below TC = 15 K and
coexists with AFM. Below TC, the static Fe moment is reduced and a 4 meV spin
gap develops indicating competition between coexisting SC and AFM order.Comment: 15 pages, 4 figure
On Traversable Lorentzian Wormholes in the Vacuum Low Energy Effective String Theory in Einstein and Jordan Frames
Three new classes (II-IV) of solutions of the vacuum low energy effective
string theory in four dimensions are derived. Wormhole solutions are
investigated in those solutions including the class I case both in the Einstein
and in the Jordan (string) frame. It turns out that, of the eight classes of
solutions investigated (four in the Einstein frame and four in the
corresponding string frame), massive Lorentzian traversable wormholes exist in
five classes. Nontrivial massless limit exists only in class I Einstein frame
solution while none at all exists in the string frame. An investigation of test
scalar charge motion in the class I solution in the two frames is carried out
by using the Plebanski-Sawicki theorem. A curious consequence is that the
motion around the extremal zero (Keplerian) mass configuration leads, as a
result of scalar-scalar interaction, to a new hypothetical "mass" that confines
test scalar charges in bound orbits, but does not interact with neutral test
particles.Comment: 18 page
Brans-Dicke wormholes in the Jordan and Einstein frames
We examine the possibility of static wormhole solutions in the vacuum
Brans-Dicke theory both in the original (Jordan) frame and in the conformally
rescaled (Einstein) frame. It turns out that, in the former frame, wormholes
exist only in a very narrow interval of the coupling parameter, viz.,
-3/2<omega<-4/3. It is shown that these wormholes are not traversable in
practice. In the latter frame, wormhole solutions do not exist at all unless
energy conditions are violated by hand.Comment: Minor errors corrected, uploaded for the benefit of the researcher
Scaling of NonOhmic Conduction in Strongly Correlated Systems
A new scaling formalism is used to analyze nonlinear I-V data in the vicinity
of metal-insulator transitions (MIT) in five manganite systems. An exponent,
called the nonlinearity exponent, and an onset field for nonlinearity, both
characteristic of the system under study, are obtained from the analysis. The
onset field is found to have an anomalously low value corroborating the
theoretically predicted electronically soft phases. The scaling functions above
and below the MIT of a polycrystalline sample are found to be the same but with
different exponents which are attributed to the distribution of the MIT
temperatures. The applicability of the scaling in manganites underlines the
universal response of the disordered systems to electric field
Intraoperative ultrasound in brain tumor surgery: A review and implementation guide.
Accurate and reliable intraoperative neuronavigation is crucial for achieving maximal safe resection of brain tumors. Intraoperative MRI (iMRI) has received significant attention as the next step in improving navigation. However, the immense cost and logistical challenge of iMRI precludes implementation in most centers worldwide. In comparison, intraoperative ultrasound (ioUS) is an affordable tool, easily incorporated into existing theatre infrastructure, and operative workflow. Historically, ultrasound has been perceived as difficult to learn and standardize, with poor, artifact-prone image quality. However, ioUS has dramatically evolved over the last decade, with vast improvements in image quality and well-integrated navigation tools. Advanced techniques, such as contrast-enhanced ultrasound (CEUS), have also matured and moved from the research field into actual clinical use. In this review, we provide a comprehensive and pragmatic guide to ioUS. A suggested protocol to facilitate learning ioUS and improve standardization is provided, and an outline of common artifacts and methods to minimize them given. The review also includes an update of advanced techniques and how they can be incorporated into clinical practice
Suppression of antiferromagnetic order and orthorhombic distortion in superconducting Ba(Fe0.961Rh0.039)2As2
Neutron diffraction and high-resolution x-ray diffraction studies find that,
similar to the closely related underdoped Ba(Fe[1-x]Cox)2As2 superconducting
compounds, Ba(Fe0.961Rh0.039)2As2 shows strong evidence of competition and
coexistence between superconductivity and antiferromagnetic order below the
superconducting transition, Tc = 14 K. The transition temperatures for both the
magnetic order and orthorhombic distortion are in excellent agreement with
those inferred from resistivity measurements, and both order parameters
manifest a distinct decrease in magnitude below Tc. These data suggest that the
strong interaction between magnetism and superconductivity is a general feature
of electron-doped Ba(Fe[1-x]TMx)2As2 superconductors (TM = Transition Metal).Comment: 4 pages, 4 figure
Photoionization in the time and frequency domain
Ultrafast processes in matter, such as the electron emission following light
absorption, can now be studied using ultrashort light pulses of attosecond
duration (s) in the extreme ultraviolet spectral range. The lack of
spectral resolution due to the use of short light pulses may raise serious
issues in the interpretation of the experimental results and the comparison
with detailed theoretical calculations. Here, we determine photoionization time
delays in neon atoms over a 40 eV energy range with an interferometric
technique combining high temporal and spectral resolution. We spectrally
disentangle direct ionization from ionization with shake up, where a second
electron is left in an excited state, thus obtaining excellent agreement with
theoretical calculations and thereby solving a puzzle raised by seven-year-old
measurements. Our experimental approach does not have conceptual limits,
allowing us to foresee, with the help of upcoming laser technology, ultra-high
resolution time-frequency studies from the visible to the x-ray range.Comment: 5 pages, 4 figure
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