3,148 research outputs found
Surface free energy of the open XXZ spin-1/2 chain
We study the boundary free energy of the XXZ spin-\tf{1}{2} chain subject
to diagonal boundary fields. We first show that the representation for its
finite Trotter number approximant obtained by Bortz, Frahm and G\"{o}hmann is
related to the partition function of the six-vertex model with reflecting ends.
Building on the Tsuchiya determinant representation for the latter quantity we
are able to take the infinite Trotter number limit. This yields a
representation for the surface free energy which involves the solution of the
non-linear integral equation that governs the thermodynamics of the XXZ
spin-1/2 chain subject to periodic boundary conditions. We show that this
integral representation allows one to extract the low- asymptotic behavior
of the boundary magnetization at finite external magnetic field on the one hand
and numerically plot this function on the other hand.Comment: 35 pages, 11 figures, V3: some new plots adde
Aero-acoustic tests of duct-burning turbofan exhaust nozzles
The acoustic and aerodynamic characteristics of several exhaust systems suitable for duct burning turbofan engines are evaluated. Scale models representing unsuppressed coannular exhaust systems are examined statically under varying exhaust conditions. Ejectors with both hardwall and acoustically treated inserts are investigated
Flight effects on the aerodynamic and acoustic characteristics of inverted profile coannular nozzles
The effect of forward flight on the jet noise of coannular exhaust nozzles, suitable for Variable Stream Control Engines (VSCE), was investigated in a series of wind tunnel tests. The primary stream properties were maintained constant at 300 mps and 394 K. A total of 230 acoustic data points was obtained. Force measurement tests using an unheated air supply covered the same range of tunnel speeds and nozzle pressure ratios on each of the nozzle configurations. A total of 80 points was taken. The coannular nozzle OASPL and PNL noise reductions observed statically relative to synthesized values were basically retained under simulated flight conditions. The effect of fan to primary stream area ratio on flight effects was minor. At take-off speed, the peak jet noise for a VSCE was estimated to be over 6 PNdB lower than the static noise level. High static thrust coefficients were obtained for the basic coannular nozzles, with a decay of 0.75 percent at take-off speeds
Flight effects on the aero/acoustic characteristics of inverted profile coannular nozzles
The effect of simulated flight speed on the acoustic and aerodynamic characteristics of coannular nozzles is examined. The noise and aerodynamic performance of the coannular nozzle exhaust systems over a large range of operating flight conditions is presented. The jet noise levels of the coannular nozzles are discussed. The impact of fan to primary nozzle area ratio and the presence of an ejector on flight effects are investigated. The impact of flight speed on the individual components of the coannular jet noise was ascertained
Aerodynamic and acoustic tests of duct-burning turbofan exhaust nozzles
The static aerodynamic and acoustic characteristics of duct-burning turbofan (DBTF) exhaust nozzles are established. Scale models, having a total area equivalent to a 0.127 m diameter convergent nozzle, simulating unsuppressed coannular nozzles and mechanically suppressed nozzles with and without ejectors (hardwall and acoustically treated) were tested in a quiescent environment. The ratio of fan to primary area was varied from 0.75 to 1.2. Far field acoustic data, perceived noise levels, and thrust measurements were obtained for 417 test conditions. Pressure ratios were varied from 1.3 to 4.1 in the fan stream and from 1.53 to 2.5 in the primary stream. Total temperature varied from 395 to 1090 K in both streams. Jet noise reductions relative to synthesized prediction from 8 PNdB (with the unsuppressed coannular nozzle) to 15 PNdB (with a mechanically suppressed configuration) were observed at conditions typical of engines being considered under the Advanced Supersonic Technology program. The inherent suppression characteristic of the unsuppressed coannular nozzle is related to the rapid mixing in the jet wake caused by the velocity profiles associated with the DBTF. Since this can be achieved without a mechanical suppressor, significant reductions in aircraft weight or noise footprint can be realized
Non-Hermitian Dynamics in the Quantum Zeno Limit
Measurement is one of the most counter-intuitive aspects of quantum physics.
Frequent measurements of a quantum system lead to quantum Zeno dynamics where
time evolution becomes confined to a subspace defined by the projections.
However, weak measurement performed at a finite rate is also capable of locking
the system into such a Zeno subspace in an unconventional way: by Raman-like
transitions via virtual intermediate states outside this subspace, which are
not forbidden. Here, we extend this concept into the realm of non-Hermitian
dynamics by showing that the stochastic competition between measurement and a
system's own dynamics can be described by a non-Hermitian Hamiltonian. We
obtain an analytic solution for ultracold bosons in a lattice and show that a
dark state of the tunnelling operator is a steady state in which the
observable's fluctuations are zero and tunnelling is suppressed by destructive
matter-wave interference. This opens a new venue of investigation beyond the
canonical quantum Zeno dynamics and leads to a new paradigm of competition
between global measurement backaction and short-range atomic dynamics.Comment: Accepted in Phys. Rev.
Multipartite Entangled Spatial Modes of Ultracold Atoms Generated and Controlled by Quantum Measurement
We show that the effect of measurement back-action results in the generation
of multiple many-body spatial modes of ultracold atoms trapped in an optical
lattice, when scattered light is detected. The multipartite mode entanglement
properties and their nontrivial spatial overlap can be varied by tuning the
optical geometry in a single setup. This can be used to engineer quantum states
and dynamics of matter fields. We provide examples of multimode generalizations
of parametric down-conversion, Dicke, and other states, investigate the
entanglement properties of such states, and show how they can be transformed
into a class of generalized squeezed states. Further, we propose how these
modes can be used to detect and measure entanglement in quantum gases.Comment: 6 Pages, 3 Figures, Supplemental Material include
Weather Indicators and Crop Yields Analysis with Wavelets
This paper presents a case study and methods for trend and periodicity identification and for forecasting which are useful for determining the impact of weather factors to crop yields. These methods combine standard approaches with wavelet analysis in order to improve the results. Hence, a brief introduction to wavelet theory is included. All analyses provided in this research are conducted on United States weather and crop yields data. Where applicable, the results obtained with the use of standard methods are compared with those which are enforced by application of the wavelet transform, illustrated with examples, and evaluated
On-farm control measures for the reduction of Salmonellosis in pigs
A longitudinal study of the prevalence of Salmonella spp. was carried out on 12 Irish pig farms, which included farrow-to-finish herds and specialised finishing units. The main objective of the project was to evaluate the efficacy of control measures implemented at farm level on highly infected farms. Control measures included the use of in-feed additives and /or improved hygiene and biosecurity measures
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