26,122 research outputs found
Ordered structures and jet noise
A series of measurements of near field pressures and turbulent velocity fluctuations were made in a jet having a Reynolds number of about 50,000 in order to investigate more quantitatively the character and behavior of the large scale structures, and to ascertain their importance to the jet noise problem. It was found that the process of interaction between vortices can be inhibited by artificially exciting the shear layers with periodic disturbances of certain frequency. The turbulent fluctuation amplitudes measured at four diameters downstream decreased considerably. Finally, it was observed that the passage frequency of the structures decreased with x in a similar manner as the frequency corresponding to the maximum intensity radiation emanating from the same value of x
Staff Pay Levels for Selected Positions in Senators’ Offices, FY2009-FY2013
[Excerpt] This report provides pay data for 16 staff position titles that are typically deployed in Senators’ offices. The positions include the following: Administrative Director; Casework Supervisor; Caseworker; Chief of Staff; Communications Director; Counsel; Executive Assistant; Field Representative; Legislative Assistant; Legislative Correspondent; Legislative Director; Press Secretary; Scheduler; “Specials Director,” a combined category that includes the job titles Director of Projects, Director of Special Projects, Director of Federal Projects, Director of Grants, Projects Director, or Grants Director; Staff Assistant; and State Director. Senators’ staff pay data for the years FY2009-FY2013 were derived from a random sampling of Senators’ offices in which at least one staff member worked in a position in each year
Staff Pay Levels for Selected Positions in House Member Offices, 2009-2013
[Excerpt] This report provides pay data for 13 staff position titles that are typically deployed in the offices of Members of the House. The positions include the following: Caseworker; Chief of Staff; Counsel; District Director; Executive Assistant; Field Representative; Legislative Assistant; Legislative Correspondent; Legislative Director; Office Manager; Press Secretary; Scheduler; and Staff Assistant. House Member staff pay data for the years 2009-2013 were developed based on a random sampling of staff for each position in each year
Complete elimination of nonlinear light-matter interactions with broadband ultrafast laser pulses
The absorption of a single photon that excites a quantum system from a low to
a high energy level is an elementary process of light-matter interaction, and a
route towards realizing pure single-photon absorption has both fundamental and
practical implications in quantum technology. Due to nonlinear optical effects,
however, the probability of pure single-photon absorption is usually very low,
which is particularly pertinent in the case of strong ultrafast laser pulses
with broad bandwidth. Here we demonstrate theoretically a counterintuitive
coherent single-photon absorption scheme by eliminating nonlinear interactions
of ultrafast laser pulses with quantum systems. That is, a completely linear
response of the system with respect to the spectral energy density of the
incident light at the transition frequency can be obtained for all transition
probabilities between 0 and 100% in a multi-level quantum systems. To that end,
a new multi-objective optimization algorithm is developed to find an optimal
spectral phase of an ultrafast laser pulse, which is capable of eliminating all
possible nonlinear optical responses while maximizing the probability of
single-photon absorption between quantum states. This work not only deepens our
understanding of light-matter interactions, but also offers a new way to study
photophysical and photochemical processes in the "absence" of nonlinear optical
effects.Comment: 11 pages, 5 figure
Program to Optimize Simulated Trajectories (POST). Volume 1: Formulation manual
A general purpose FORTRAN program for simulating and optimizing point mass trajectories (POST) of aerospace vehicles is described. The equations and the numerical techniques used in the program are documented. Topics discussed include: coordinate systems, planet model, trajectory simulation, auxiliary calculations, and targeting and optimization
Homodyne locking of a squeezer
We report on the successful implementation of a new approach to locking the
frequencies of an OPO-based squeezed-vacuum source and its driving laser. The
technique allows the simultaneous measurement of the phase-shifts induced by a
cavity, which may be used for the purposes of frequency-locking, as well as the
simultaneous measurement of the sub-quantum-noise-limited (sub-QNL) phase
quadrature output of the OPO. The homodyne locking technique is cheap, easy to
implement and has the distinct advantage that subsequent homodyne measurements
are automatically phase-locked. The homodyne locking technique is also unique
in that it is a sub-QNL frequency discriminator.Comment: Accepted to Optics Letter
Single-machine scheduling with stepwise tardiness costs and release times
We study a scheduling problem that belongs to the yard operations component of the railroad planning problems, namely the hump sequencing problem. The scheduling problem is characterized as a single-machine problem with stepwise tardiness cost objectives. This is a new scheduling criterion which is also relevant in the context of traditional machine scheduling problems. We produce complexity results that characterize some cases of the problem as pseudo-polynomially solvable. For the difficult-to-solve cases of the problem, we develop mathematical programming formulations, and propose heuristic algorithms. We test the formulations and heuristic algorithms on randomly generated single-machine scheduling problems and real-life datasets for the hump sequencing problem. Our experiments show promising results for both sets of problems
A delta Scuti distance to the Large Magellanic Cloud
We present results from a well studied delta Scuti star discovered in the
LMC. The absolute magnitude of the variable was determined from the PL relation
for Galactic delta Scuti stars and from the theoretical modeling of the
observed B,V,I light curves. The two methods give distance moduli for the LMC
of 18.46+-0.19 and 18.48+-0.15, respectively, for a consistent value of the
stellar reddening of E(B-V)=0.08+-0.02. We have also analyzed 24 delta Scuti
candidates discovered in the OGLE II survey of the LMC, and 7 variables
identified in the open cluster LW 55 and in the galaxy disk by Kaluzny et al.
(2003, 2006). We find that the LMC delta Scuti stars define a PL relation whose
slope is very similar to that defined by the Galactic delta Scuti variables,
and yield a distance modulus for the LMC of 18.50+-0.22 mag. We compare the
results obtained from the delta Scuti variables with those derived from the LMC
RR Lyrae stars and Cepheids. Within the observational uncertainties, the three
groups of pulsating stars yield very similar distance moduli. These moduli are
all consistent with the "long" astronomical distance scale for the Large
Magellanic Cloud.Comment: Accepted for publication on A
- …