4,487 research outputs found
Simplified landscapes for optimization of shaken lattice interferometry
Motivated by recent results using shaken optical lattices to perform atom
interferometry, we explore splitting of an atom cloud trapped in a
phase-modulated ("shaken") optical lattice. Using a simple analytic model we
are able to show that we can obtain the simplest case of splitting via single-frequency shaking. This is confirmed both
via simulation and experiment. Furthermore, we are able to split with a
relative phase between the two split arms of or depending on
our shaking frequency. Addressing higher-order splitting, we determine that
splitting is sufficient to be able to accelerate the
atoms in counter-propagating lattices. Finally, we show that we can use a
genetic algorithm to optimize and splitting to within by restricting our
optimization to the resonance frequencies corresponding to single- and
two-photon transitions between Bloch bands
Justice Jackson and the Judicial Function
Much of the pattern of division in the present Supreme Court is traceable to basic differences of opinion regarding the proper role of a judge in the process of constitutional adjudication. Some students of the Court, yielding to the current fashion of reducing even intricate problems to capsule terms, have tried to explain the controversy by classifying the justices as either liberals or conservatives. A second school poses the disagreement largely in terms of judicial activism as opposed to judicial restraint. It is this view that has the greater relevance for the present discussion. C.H. Pritchett, one of the leading exponents of this view, says that the judicial activist appears to experience a deep sense of personal responsibility for the immediate consequences of his judicial decisions. He feels that the Court has a range of discretion, that there are alternatives available to him, and that he must make the choice which will give the right result. The activist does not pretend to exercise the power of judicial review in accordance with standards imposed by the legal system; he will apply formal legal concepts only if they assist him in reaching a desirable goal. On the present Court, Pritchett suggests, Justices Black and Douglas best reflect this goal-orientation of the activists. The proponents of judicial self-restraint see a justice at his best when he exercises the judicial power with restraint and prudence. This functionally- oriented view sees the Court not as crusader or advocate but as one of the instruments of political and social accommodation and adjustment in a complicated governmental system. Its stress is not on securing a result conforming to the jurist\u27s own scheme of values but upon adherence to appropriate judicial standards and proper manipulation of judicial techniques. Justice Frankfurter, Pritchett submits, is the modem leader of the restraint school, and his views are subjected to close scrutiny.
While Pritchett\u27s approach is basically sound, it does have the effect of obscuring the constitutional views of Justice Robert H. Jackson, who often seems to be regarded as a mere intellectual appendage of Justice Frankfurter. In contrast to his elaborate analysis of Frankfurter\u27s conception of the judicial function, Pritchett, writing before Jackson\u27s death, summarized Jackson\u27s judicial philosophy only briefly and then concluded, The unpredictability of Jackson\u27s performance leads one to question whether he has developed any systematic theories about . . . the judicial function. This cursory conclusion suggests the need for a deeper penetration into the general writings and judicial opinions of Justice Jackson to discover if he had an integrated philosophy concerning the judicial function, and to appraise the extent to which he was an advocate of judicial self-restraint. This study is an attempt to fill that need. Its intent is not to summarize Justice Jackson\u27s political and judicial career; it is rather an inquiry into his conception of the judicial function as applied to certain basic types of review situations. If we can determine this, we may have the key that will enable us to interpret his Supreme Court experience
Orbiter/launch system
The system includes reusable turbojet propelled booster vehicles releasably connected to a reusable rocket powered orbit vehicle. The coupled orbiter-booster combination takes off horizontally and ascends to staging altitude and speed under booster power with both orbiter and booster wings providing lift. After staging, the booster vehicles fly back to Earth for horizontal landing and the orbiter vehicle continues ascending to orbit
Escaping stars from young low-N clusters
With the use of N-body calculations the amount and properties of escaping
stars from low-N (N = 100 and 1000) young embedded star clusters prior to gas
expulsion are studied over the first 5 Myr of their existence. Besides the
number of stars also different initial radii and binary populations are
examined as well as virialised and collapsing clusters. It is found that these
clusters can loose substantial amounts (up to 20%) of stars within 5 Myr with
considerable velocities up to more than 100 km/s. Even with their mean
velocities between 2 and 8 km/s these stars will still be travelling between 2
and 30 pc during the 5 Myr. Therefore can large amounts of distributed stars in
star-forming regions not necessarily be counted as evidence for the isolated
formation of stars.Comment: 10 pages, 10 figures, accepted for publication by MNRA
Flow establishment in a generic scramjet combustor
The establishment of a quasi-steady flow in a generic scramjet combustor was studied for the case of a time varying inflow to the combustor. Such transient flow is characteristic of the reflected shock tunnel and expansion tube test facilities. Several numerical simulations of hypervelocity flow through a straight duct combustor with either a side wall step fuel injector or a centrally located strut injector are presented. Comparisons were made between impulsively started but otherwise constant flow conditions (typical of the expansion tube or tailored operations of the reflected shock tunnel) and the relaxing flow produced by the 'undertailored' operations of the reflected shock tunnel. Generally the inviscid flow features, such as the shock pattern and pressure distribution, were unaffected by the time varying inlet conditions and approached steady state in approx. the times indicated by experimental correlations. However, viscous features, such as heat transfer and skin friction, were altered by the relaxing inlet flow conditions
Properties of hierarchically forming star clusters
We undertake a systematic analysis of the early (< 0.5 Myr) evolution of
clustering and the stellar initial mass function in turbulent fragmentation
simulations. These large scale simulations for the first time offer the
opportunity for a statistical analysis of IMF variations and correlations
between stellar properties and cluster richness. The typical evolutionary
scenario involves star formation in small-n clusters which then progressively
merge; the first stars to form are seeds of massive stars and achieve a
headstart in mass acquisition. These massive seeds end up in the cores of
clusters and a large fraction of new stars of lower mass is formed in the outer
parts of the clusters. The resulting clusters are therefore mass segregated at
an age of 0.5 Myr, although the signature of mass segregation is weakened
during mergers. We find that the resulting IMF has a smaller exponent
(alpha=1.8-2.2) than the Salpeter value (alpha=2.35). The IMFs in subclusters
are truncated at masses only somewhat larger than the most massive stars (which
depends on the richness of the cluster) and an universal upper mass limit of
150 Msun is ruled out. We also find that the simulations show signs of the
IGIMF effect proposed by Weidner & Kroupa, where the frequency of massive stars
is suppressed in the integrated IMF compared to the IMF in individual clusters.
We identify clusters through the use of a minimum spanning tree algorithm which
allows easy comparison between observational survey data and the predictions of
turbulent fragmentation models. In particular we present quantitative
predictions regarding properties such as cluster morphology, degree of mass
segregation, upper slope of the IMF and the relation between cluster richness
and maximum stellar mass. [abridged]Comment: 21 Pages, 25 Figure
Star Formation in a Cosmological Simulation of Reionization
We study the luminosity functions of high-redshift galaxies in detailed
hydrodynamic simulations of cosmic reionization, which are designed to
reproduce the evolution of the Lyman-alpha forest between z=5 and z=6. We find
that the luminosity functions and total stellar mass densities are in agreement
with observations when plausible assumptions about reddenning at z=6 are made.
Our simulations support the conclusion that stars alone reionized the universe.Comment: Accepted for publication in Ap
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