19,910 research outputs found
Model-Independent Predictions for Low Energy Isoscalar Heavy Baryon Observables in the Combined Heavy Quark and Large Expansion
Model-independent predictions for excitation energies, semileptonic form
factors and electromagnetic decay rates of isoscalar heavy baryons and their
low energy excited states are discussed in terms of the combined heavy quark
and large expansion. At leading order, the observables are completely
determined in terms of the known excitation energy of the first excited state
of . At next-to-leading order in the combined expansion all heavy
baryon observables can be expressed in a model-independent way in terms of two
experimentally measurable quantities. We list predictions at leading and
next-to-leading order.Comment: 7 pages, LaTe
Excited Heavy Baryons and Their Symmetries III: Phenomenology
Phenomenological applications of an effective theory of low-lying excited
states of charm and bottom isoscalar baryons are discussed at leading and
next-to-leading order in the combined heavy quark and large expansion.
The combined expansion is formulated in terms of the counting parameter
; the combined expansion is in powers of
. We work up to next-to-leading order. We obtain
model-independent predictions for the excitation energies, the semileptonic
form factors and electromagnetic decay rates. The spin-averaged mass of the
doublet of the first orbitally excited sate of is predicted to be
approximately . It is shown that in the combined limit at leading and
next-to-leading order there is only one independent form factor describing
; similarly, and
decays are described by a single independent form factor. These form factors
are calculated at leading and next-to-leading order in the combined expansion.
The electromagnetic decay rates of the first excited states of and
are determined at leading and next-to leading order. The ratio of
radiative decay rates is predicted to be approximately
0.2, greatly different from the heavy quark effective theory value of unity.Comment: 21 pages, 2 figure
Large Universality of The Baryon Isgur--Wise Form Factor: The Group Theoretical Approach
In a previous article, it has been proved under the framework of chiral
soliton model that the same Isgur--Wise form factor describes the semileptonic
and decays in the
large limit. It is shown here that this result is in fact independent of
the chiral soliton model and is solely the consequence of the spin-flavor SU(4)
symmetry which arises in the baryon sector in the large limit.Comment: 10 pages in REVTeX, no figure
Reflection high-energy electron diffraction studies of the growth of lnAs/Ga_(1-x)In_xSb strained-layer superlattices
We have used reflection highâenergy electron diffraction to study the surface periodicity of the growth front of InAs/GaInSb strainedâlayer superlattices (SLSs). We found that the apparent surface lattice spacing reproducibly changed during layers which subsequent xâray measurements indicated were coherently strained. Abrupt changes in the measured streak spacings were found to be correlated to changes in the growth flux. The profile of the dynamic streak spacing was found to be reproducible when comparing consecutive periods of a SLSs or different SLSs employing the same shuttering scheme at the InAs/GaInSb interface. Finally, when the interface shuttering scheme was changed, it was found that the dynamic streak separation profile also changed. Large changes in the shuttering scheme led to dramatic differences in the streak separation profile, and small changes in the shuttering scheme led to minor changes in the profile. In both cases, the differences in the surface periodicity profile occurred during the parts of the growth where the incident fluxes differed
New negative differential resistance device based on resonant interband tunneling
We propose and demonstrate a novel negative differential resistance device based on resonant interband tunneling. Electrons in the InAs/AlSb/GaSb/AlSb/InAs structure tunnel from the InAs conduction band into a quantized state in the GaSb valence band, giving rise to a peak in the current-voltage characteristic. This heterostructure design virtually eliminates many of the competing transport mechanisms which limit the performance of conventional double-barrier structures. Peak-to-valley current ratios as high as 20 and 88 are observed at room temperature and liquid-nitrogen temperature, respectively. These are the highest values reported for any tunnel structure
Observation of large peak-to-valley current ratios and large peak current densities in AlSb/InAs/AlSb double-barrier tunnel structures
We report improved peak-to-valley current ratios and peak current densities in InAs/AlSb double-barrier, negative differential resistance tunnel structures. Our peak-to-valley current ratios are 2.9 at room temperature and 10 at liquid-nitrogen temperatures. Furthermore, we have observed peak current densities of 1.7Ă10^5 A/cm^2. These figures of merit are substantially better than previously reported values. The improvements are obtained by adding spacer layers near the barriers, thinner well regions, and thinner barriers
Demonstration of large peak-to-valley current ratios in InAs/AlGaSb/InAs single-barrier heterostructures
We report large peak-to-valley current ratios in InAs/AlxGa1âxSb/InAs single-barrier tunnel structures. The mechanism for single-barrier negative differential resistance (NDR) has been proposed and demonstrated recently. A peak-to-valley current ratio of 3.4 (1.2) at 77 K (295 K), which is substantially larger than what has been previously reported, was observed in a 200-Ă
-thick Al0.42Ga0.58Sb barrier. A comparison with a calculated current-voltage curve yields good agreement in terms of peak current and the slope of the NDR region. The single-barrier structure is a candidate for high-speed devices because of expected short tunneling times and a wide NDR region
Airborne Computer Technology
The development of airborne digital computer has been greatly influenced by rapid technological advances. This paper provides an overview of the present status and the direction of further evolution. It discusses the changes that are taking place in the areas of hardware, software and computer organization; and suggests a number of approaches towards a broadened usage of airborne computer to take advantage of its increasing capability and decreasing cost
The Sovereign Nation of Hawai\u27i: Resistance in the Legacy of Aloha \u27Oe
The song âAloha âOeâ is celebrated throughout the nation of Hawaiâi as a representation of traditional Hawaiian culture, written over a century ago by the last reigning monarch of the islands, Queen Liliâuokalani. Though the song was initially composed as a mele hoâoipoipo (love song), over the years it has been socially, politically, and culturally redefined by Kanaka Maoli (Native Hawaiians) into a song of melancholic farewell between the Queen and her kingdom, and the people with their land. Why did âAloha âOeâ experience an upsurge in popularity after each of the exercises of colonial power over Hawaiâi, regardless of Liliâuokalaniâs insistence that the composition is a love song? I seek to explore the history of native Hawaiian resistance towards colonial U.S. forces as well as present-day resistance of ongoing settler colonialism through the framework of analyzing Queen Liliâuokalaniâs composition, âAloha âOe.â I argue that the resignification of this song is a reaction against colonial forces erasing the sovereign rights of Liliâuokalani in and beyond Hawaiâi, and artists who continue to perform âAloha âOeâ today sustain resistance in the form of Native counter-hegemonies. Through my interdisciplinary and constructivist approach, focusing on primary source literature and music as well as secondary sources of Hawaiian cultural history, I will demonstrate that the legacy of this song as it continues to resonate today in performance art represents the continual resistance to and denial of colonization
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