21,228 research outputs found
Method for the preparation of thin-skinned asymmetric reverse osmosis membranes and products thereof
A method for preparing water insoluble asymmetric membranes from water soluble polymers is discussed. The process involves casting a film of the polymer, partially drying it, and then contacting it with a concentrated solution of a transition metal salt. The transition metal ions render the polymer insoluable and are believed to form a complex with it. Optionally, the polymer is crosslinked with heat or radiation. The most preferred polymer is poly(vinyl alcohol). The most preferred complexing salt is copper sulfate. The process and the metal ion linked membranes are discussed. The membranes are reverse osmosis membranes
The status of pentaquark spectroscopy on the lattice
The present work is a summary of the status of lattice pentaquark
calculations. After a pedagogic introduction to the basics of lattice hadron
spectroscopy we give a critical comparison of results presently available in
the literature. Special emphasis is put on presenting some of the possible
pitfalls of these calculations. In particular we discuss at length the choice
of the hadronic operators and the separation of genuine five-quark states from
meson-baryon scattering states.Comment: 13 pages LaTeX, 1 eps figur
F-15 flight flutter test program
The modes to be observed during the F-15 flight flutter test program were selected on the basis of the results of analytical studies, wind tunnel tests, and ground vibration tests. The modes (both symmetrical and antisymmetrical) tracked on this basis were: fin first bending, fin torsion, fin tip roll, stabilator bending, stabilator pitch, boom lateral bending, boom torsion, boom vertical bending, wing first bending, wing second bending, wing first torsion, outer wing torsion, and aileron rotation. Data obtained for these various modes were evaluated in terms of damping versus airspeed at 1525 m (5000 ft), damping versus altitude at the cross-section Mach numbers (to extrapolate to the damping value to be expected at sea level), and flutter boundaries on the basis of flutter margin of various modal pairs representing potential flutter mechanisms. Results of these evaluations are summarized in terms of minimum predicted flutter margin for the various mechanisms
Pentaquark hadrons from lattice QCD
We study spin 1/2 isoscalar and isovector candidates in both parity channels
for the recently discovered \Theta^+(1540) pentaquark particle in quenched
lattice QCD. Our analysis takes into account all possible uncertainties, such
as statistical, finite size and quenching errors when performing the chiral and
continuum extrapolations and we have indications that our signal is separated
from scattering states. The lowest mass that we find in the I^P=0^- channel is
in complete agreement with the experimental value of the \Theta^+ mass. On the
other hand, the lowest mass state in the opposite parity I^P=0^+ channel is
much higher. Our findings suggests that the parity of the \Theta^+ is negative.Comment: 13 pages, 5 figures. Final version, appeared in JHE
Synthesizing Imperative Programs from Examples Guided by Static Analysis
We present a novel algorithm that synthesizes imperative programs for
introductory programming courses. Given a set of input-output examples and a
partial program, our algorithm generates a complete program that is consistent
with every example. Our key idea is to combine enumerative program synthesis
and static analysis, which aggressively prunes out a large search space while
guaranteeing to find, if any, a correct solution. We have implemented our
algorithm in a tool, called SIMPL, and evaluated it on 30 problems used in
introductory programming courses. The results show that SIMPL is able to solve
the benchmark problems in 6.6 seconds on average.Comment: The paper is accepted in Static Analysis Symposium (SAS) '17. The
submission version is somewhat different from the version in arxiv. The final
version will be uploaded after the camera-ready version is read
Formal Verification of Neural Network Controlled Autonomous Systems
In this paper, we consider the problem of formally verifying the safety of an
autonomous robot equipped with a Neural Network (NN) controller that processes
LiDAR images to produce control actions. Given a workspace that is
characterized by a set of polytopic obstacles, our objective is to compute the
set of safe initial conditions such that a robot trajectory starting from these
initial conditions is guaranteed to avoid the obstacles. Our approach is to
construct a finite state abstraction of the system and use standard
reachability analysis over the finite state abstraction to compute the set of
the safe initial states. The first technical problem in computing the finite
state abstraction is to mathematically model the imaging function that maps the
robot position to the LiDAR image. To that end, we introduce the notion of
imaging-adapted sets as partitions of the workspace in which the imaging
function is guaranteed to be affine. We develop a polynomial-time algorithm to
partition the workspace into imaging-adapted sets along with computing the
corresponding affine imaging functions. Given this workspace partitioning, a
discrete-time linear dynamics of the robot, and a pre-trained NN controller
with Rectified Linear Unit (ReLU) nonlinearity, the second technical challenge
is to analyze the behavior of the neural network. To that end, we utilize a
Satisfiability Modulo Convex (SMC) encoding to enumerate all the possible
segments of different ReLUs. SMC solvers then use a Boolean satisfiability
solver and a convex programming solver and decompose the problem into smaller
subproblems. To accelerate this process, we develop a pre-processing algorithm
that could rapidly prune the space feasible ReLU segments. Finally, we
demonstrate the efficiency of the proposed algorithms using numerical
simulations with increasing complexity of the neural network controller
Generalized mean-field study of a driven lattice gas
Generalized mean-field analysis has been performed to study the ordering
process in a half-filled square lattice-gas model with repulsive nearest
neighbor interaction under the influence of a uniform electric field. We have
determined the configuration probabilities on 2-, 4-, 5-, and 6-point clusters
excluding the possibility of sublattice ordering. The agreement between the
results of 6-point approximations and Monte Carlo simulations confirms the
absence of phase transition for sufficiently strong fields.Comment: 4 pages (REVTEX) with 4 PS figures (uuencoded
Experiment K-6-01. Distribution and biochemistry of mineral and matrix in the femurs of rats
Previous analyses of the composition of mineral and matrix in the bone of young rats following space flight has revealed deficits in calcium, phosphorus, and osteocalcin, a non-collagenous protein, without an associated decrease in collagen. To characterize the location and nature of this mineralization defect in a weight bearing long bone, the femur, researchers attempted to relate the spatial distribution of mineral in situ in the proximal, central and distal thirds of the femoral diaphysis to the biochemical composition of bone from the same area. Biochemical analyses revealed lower concentrations of calcium, phosphorus and osteocalcin but not collagen only in the central third of the diaphysis of the flight animals (F) compared to synchronous controls (S). Collagen concentration was reduced only in the proximal third of the diaphysis, where all 3 crosslinks, expressed as nM/mol collagen were higher in F than S. A new technique, x ray microtomography, with a resolution of 26 microns, was used to obtain semi-quantitative data on mineral distribution in reconstructed sections of wet whole bone. To improve the resolution of the mineral density distribution, images of the surfaces of cut sections were analyzed by backscattered electrons in a scanning electron microscope (BSE). There was good agreement between the results of the two stereochemical techniques which revealed distinct patterns of mineralization in transverse and longitudinal directions of the diaphysis. The novel methodology developed for this flight experiment shows considerable promise in elucidating the biochemical nature of what appear to be regional alterations in the mineralization of long bones of animals exposed to spaceflight
Optically-Induced Polarons in Bose-Einstein Condensates: Monitoring Composite Quasiparticle Decay
Nonresonant light-scattering off atomic Bose-Einstein condensates (BECs) is
predicted to give rise to hitherto unexplored composite quasiparticles:
unstable polarons, i.e., local ``impurities'' dressed by virtual phonons.
Optical monitoring of their spontaneous decay can display either Zeno or
anti-Zeno deviations from the Golden Rule, and thereby probe the temporal
correlations of elementary excitations in BECs.Comment: 4 pages, 3 figure
- …