6,946 research outputs found
Propellant tank pressurization system Patent
Method and apparatus for pressurizing propellant tanks used in propulsion motor feed syste
An investigation of cotton for parachute cloth
This is a resume of the work of the Bureau of Standards on a cotton parachute cloth for use as a substitute for silk in the event of an emergency curtailing the supply. Cotton yarn of high strength in proportion to its weight and otherwise specially suitable for parachute cloth was developed. Cloth woven from this yarn in the bureau mill was equal or superior to parachute silk in strength and tear resistance, met the requirements with respect to air permeability, and weighed only a few tenths of an ounce per square yard more than the silk cloth. Practical trials of cotton parachutes carried out by the Navy Department clearly indicate that the cotton parachute closely approaches the silk parachute in performance as to rate of descent, opening time, strength and ability to function when stored in the pack for sixty days. The increase in weight of the equipment resulting from the use of cotton cloth instead of silk is considered to be well within practicable limits. A specification for cotton parachute cloth and the way in which the requirements of the specification have been met are given. Cotton yarns suitable for parachute cloth are now being woven commercially in the United States
Spin squeezing of atomic ensembles by multi-colour quantum non-demolition measurements
We analyze the creation of spin squeezed atomic ensembles by simultaneous
dispersive interactions with several optical frequencies. A judicious choice of
optical parameters enables optimization of an interferometric detection scheme
that suppresses inhomogeneous light shifts and keeps the interferometer
operating in a balanced mode that minimizes technical noise. We show that when
the atoms interact with two-frequency light tuned to cycling transitions the
degree of spin squeezing scales as where is the
resonant optical depth of the ensemble. In real alkali atoms there are loss
channels and the scaling may be closer to Nevertheless
the use of two-frequencies provides a significant improvement in the degree of
squeezing attainable as we show by quantitative analysis of non-resonant
probing on the Cs D1 line. Two alternative configurations are analyzed: a
Mach-Zehnder interferometer that uses spatial interference, and an interaction
with multi-frequency amplitude modulated light that does not require a spatial
interferometer.Comment: 7 figure
A new proof that alternating links are non-trivial
We use a simple geometric argument and small cancellation properties of link
groups to prove that alternating links are non-trivial. This proof uses only
classic results in topology and combinatorial group theory.Comment: Minor changes. To appear in Fundamenta Mathematica
Continuous loading of S calcium atoms into an optical dipole trap
We demonstrate an efficient scheme for continuous trap loading based upon
spatially selective optical pumping. We discuss the case of S
calcium atoms in an optical dipole trap (ODT), however, similar strategies
should be applicable to a wide range of atomic species. Our starting point is a
reservoir of moderately cold (K) metastable
P-atoms prepared by means of a magneto-optic trap (triplet-MOT). A
focused 532 nm laser beam produces a strongly elongated optical potential for
S-atoms with up to 350 K well depth. A weak focused laser beam
at 430 nm, carefully superimposed upon the ODT beam, selectively pumps the
P-atoms inside the capture volume to the singlet state, where they
are confined by the ODT. The triplet-MOT perpetually refills the capture volume
with P-atoms thus providing a continuous stream of cold atoms into
the ODT at a rate of s. Limited by evaporation loss, in 200 ms we
typically load atoms with an initial radial temperature of 85
K. After terminating the loading we observe evaporation during 50 ms
leaving us with atoms at radial temperatures close to 40 K and a
peak phase space density of . We point out that a
comparable scheme could be employed to load a dipole trap with
P-atoms.Comment: 4 pages, 4 figure
A low-loss, broadband antenna for efficient photon collection from a coherent spin in diamond
We report the creation of a low-loss, broadband optical antenna giving highly
directed output from a coherent single spin in the solid-state. The device, the
first solid-state realization of a dielectric antenna, is engineered for
individual nitrogen vacancy (NV) electronic spins in diamond. We demonstrate a
directionality close to 10. The photonic structure preserves the high spin
coherence of single crystal diamond (T2>100us). The single photon count rate
approaches a MHz facilitating efficient spin readout. We thus demonstrate a key
enabling technology for quantum applications such as high-sensitivity
magnetometry and long-distance spin entanglement.Comment: 5 pages, 4 figures and supplementary information (5 pages, 8
figures). Comments welcome. Further information under
http://www.quantum-sensing.physik.unibas.c
Coloring random graphs
We study the graph coloring problem over random graphs of finite average
connectivity . Given a number of available colors, we find that graphs
with low connectivity admit almost always a proper coloring whereas graphs with
high connectivity are uncolorable. Depending on , we find the precise value
of the critical average connectivity . Moreover, we show that below
there exist a clustering phase in which ground states
spontaneously divide into an exponential number of clusters and where the
proliferation of metastable states is responsible for the onset of complexity
in local search algorithms.Comment: 4 pages, 1 figure, version to app. in PR
Fermi-Polaron: Diagrammatic Monte Carlo for Divergent Sign-Alternating Series
Diagrammatic Monte Carlo approach is applied to a problem of a single
spin-down fermion resonantly interacting with the sea of ideal spin-up
fermions. On one hand, we develop a generic, sign-problem tolerant, method of
exact numerical solution of polaron-type models. On the other hand, our
solution is important for understanding the phase diagram and properties of the
BCS-BEC crossover in the strongly imbalanced regime. This is the first, and
possibly characteristic, example of how the Monte Carlo approach can be applied
to a divergent sign-alternating diagrammatic series.Comment: 4 pages, 7 figure
Reformulation of the Stochastic Potential Switching Algorithm and a Generalized Fourtuin-Kasteleyn Representation
A new formulation of the stochastic potential switching algorithm is
presented. This reformulation naturally leads us to a generalized
Fourtuin-Kasteleyn representation of the partition function Z. A formula for
internal energy E and that of heat capacity C are derived from derivatives of
the partition function. We also derive a formula for the exchange probability
in the replica exchange Monte Carlo method. By combining the formulae with the
Stochastic Cutoff method, we can greatly reduce the computational time to
perform internal energy and heat capacity measurements and the replica exchange
Monte Carlo method in long-range interacting systems. Numerical simulations in
three dimensional magnetic dipolar systems show the validity and efficiency of
the method.Comment: 11 pages, 6 figures, to appear in PR
Mobile Resource Guarantees for Smart Devices
Abstract. We present the Mobile Resource Guarantees framework: a system for ensuring that downloaded programs are free from run-time violations of resource bounds. Certificates are attached to code in the form of efficiently checkable proofs of resource bounds; in contrast to cryptographic certificates of code origin, these are independent of trust networks. A novel programming language with resource constraints encoded in function types is used to streamline the generation of proofs of resource usage.
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