1,846 research outputs found
Calibration of Distributionally Robust Empirical Optimization Models
We study the out-of-sample properties of robust empirical optimization
problems with smooth -divergence penalties and smooth concave objective
functions, and develop a theory for data-driven calibration of the non-negative
"robustness parameter" that controls the size of the deviations from
the nominal model. Building on the intuition that robust optimization reduces
the sensitivity of the expected reward to errors in the model by controlling
the spread of the reward distribution, we show that the first-order benefit of
``little bit of robustness" (i.e., small, positive) is a significant
reduction in the variance of the out-of-sample reward while the corresponding
impact on the mean is almost an order of magnitude smaller. One implication is
that substantial variance (sensitivity) reduction is possible at little cost if
the robustness parameter is properly calibrated. To this end, we introduce the
notion of a robust mean-variance frontier to select the robustness parameter
and show that it can be approximated using resampling methods like the
bootstrap. Our examples show that robust solutions resulting from "open loop"
calibration methods (e.g., selecting a confidence level regardless of
the data and objective function) can be very conservative out-of-sample, while
those corresponding to the robustness parameter that optimizes an estimate of
the out-of-sample expected reward (e.g., via the bootstrap) with no regard for
the variance are often insufficiently robust.Comment: 51 page
Schottky Barrier Engineering for Contacts in Advanced CMOS Technology
Ph.DDOCTOR OF PHILOSOPH
Prevalence of Tidal Interactions among Local Seyfert Galaxies
No mechanisms have hitherto been conclusively demonstrated to be responsible
for initiating optically-luminous nuclear (Seyfert) activity in local disk
galaxies. Only a small minority of such galaxies are visibly disturbed in
optical starlight, with the observed disturbances being at best marginally
stronger than those found in matched samples of inactive galaxies. Here, we
report the first systematic study of an optically-selected sample of
twenty-three active galaxies in atomic hydrogen (HI) gas, which is the most
sensitive and enduring tracer known of tidal interactions. Eighteen of these
galaxies are (generally) classified as Seyferts, with over half (and perhaps
all) having [OIII] luminosities within two orders of magnitude of Quasi-Stellar
Objects. Only ~28% of these Seyfert galaxies are visibly disturbed in optical
DSS2 images. By contrast, ~94% of the same galaxies are disturbed in HI, in
nearly all cases not just spatially but also kinematically on galactic (>~20
kpc) scales. In at least ~67% and perhaps up to ~94% of cases, the observed HI
disturbances can be traced to tidal interactions with neighboring galaxies
detected also in HI. The majority of these neighboring galaxies have projected
separations of <~ 100 kpc and differ in radial velocities by <~100 km/s from
their respective Seyfert galaxies, and many have optical luminosities ranging
from the Small to Large Magellanic Clouds. In a companion paper, we show that
only ~15% of a matched control sample of inactive galaxies display comparable
HI disturbances. Our results suggest that: i) most Seyfert galaxies (with high
nuclear luminosities) have experienced tidal interactions in the recent past;
ii) in most cases, these tidal interactions are responsible for initiating
events that lead to their nuclear activity.Comment: 64 pages, 44 figures, accepted for publication in ApJ. Changes:
Nothing is changed except that the paper was compiled differently to reduce
the number of pages. To be friendly to the Earth forest, you could also
choose to only print the text part of the paper and view images on line. (see
http://www.astro.virginia.edu/~ck2v/paper/
MAX 4 and MAX 5 CMB anisotropy measurement constraints on open and flat-Lambda CDM cosmogonies
We account for experimental and observational uncertainties in likelihood
analyses of cosmic microwave background (CMB) anisotropy data from the MAX 4
and MAX 5 experiments. These analyses use CMB anisotropy spectra predicted in
open and spatially-flat Lambda cold dark matter cosmogonies. Amongst the models
considered, the combined MAX data set is most consistent with the CMB
anisotropy shape in Omega_0 ~ 0.1-0.2 open models and less so with that in old
(t_0 >~ 15 - 16 Gyr, i.e., low h), high baryon density (Omega_B >~ 0.0175/h^2),
low density (Omega_0 ~ 0.2 - 0.4), flat-Lambda models. The MAX data alone do
not rule out any of the models we consider at the 2-sigma level.
Model normalizations deduced from the combined MAX data are consistent with
those drawn from the UCSB South Pole 1994 data, except for the flat bandpower
model where MAX favours a higher normalization. The combined MAX data
normalization for open models with Omega_0 ~ 0.1-0.2 is higher than the upper
2-sigma value of the DMR normalization. The combined MAX data normalization for
old (low h), high baryon density, low-density flat-Lambda models is below the
lower 2-sigma value of the DMR normalization. Open models with Omega_0 ~
0.4-0.5 are not far from the shape most favoured by the MAX data, and for these
models the MAX and DMR normalizations overlap. The MAX and DMR normalizations
also overlap for Omega_0 = 1 and some higher h, lower Omega_B, low-density
flat-Lambda models.Comment: Latex, 37 pages, uses aasms4 styl
Universal Extra Dimensions on Real Projective Plane
We propose a six dimensional Universal Extra Dimensions (UED) model
compactified on a real projective plane , a two-sphere with its antipodal
points being identified. We utilize the Randjbar-Daemi-Salam-Strathdee
spontaneous sphere compactification with a monopole configuration of an extra
gauge field that leads to a spontaneous radius stabilization. Unlike
the sphere and the so-called compactifications, the massless
gauge boson is safely projected out. We show how a compactification on a
non-orientable manifold results in a chiral four dimensional gauge theory by
utilizing 6D chiral gauge and Yukawa interactions. The resultant Kaluza-Klein
mass spectra are distinct from the ordinary UED models compactified on torus.
We briefly comment on the anomaly cancellation and also on a possible dark
matter candidate in our model.Comment: 14 pages, 1 figure (v1); Comments and references added, 15 pages
(v2); Comments and references added, 15 pages, version to appear in Phys.
Lett. B (v3
First Confirmed Detection of a Bipolar Molecular Outflow from a Young Brown Dwarf
Studying the earliest stages in the birth of stars is crucial for
understanding how they form. Brown dwarfs with masses between that of stars and
planets are not massive enough to maintain stable hydrogen-burning fusion
reactions during most of their lifetime. Their origins are subject to much
debate in recent literature because their masses are far below the typical mass
where core collapse is expected to occur. We present the first confirmed
evidence that brown dwarfs undergo a phase of molecular outflow that is typical
of young stars. Using the Submillimeter Array, we have obtained a map of a
bipolar molecular outflow from a young brown dwarf. We estimate an outflow mass
of 1.6 x 10^-4 M_Sun and a mass-loss rate of 1.4 x 10^-9 M_Sun. These values
are over two orders of magnitude smaller than the typical ones for T Tauri
stars. From our millimiter continuum data and our own analysis of Spitzer
infrared photometry, we estimate that the brown dwarf has a disk with a mass of
8 x 10^-3 M_Sun and an outer disk radius of 80 AU. Our results demonstrate that
the bipolar molecular outflow operates down to planetary masses, occurring in
brown dwarfs as a scaled-down version of the universal process seen in young
stars.Comment: accepted by ApJ Letter
Suspected neonatal isoerythrolysis with concurrent Actinomyces hyovaginalis in a foal
Objectives: This case report aimed at diagnosing and instituting timely intervention to avert Neonatal Isoerythrolysis with concurrent infections in foals. Material and Methods: Baby Dokki is a one day old, filly, foal, pony cross, weighing about 20kg. She is managed in a stable with its dam. Baby Dokki was found dead a day after her birth. Post mortem examination revealed a generalized jaundice in the mucous membrane, muscles and aorta. Besides that, the synovial fluids were also thicken and yellowish. As well, the large intestine contains very hard greenish fecal material obstructing the rectum. Softer yellowish fecal material was found to be impacted dorsal to the hard fecal material. Results: Furthermore, the bacteriology result divulged the presence of Actinomyces hyovaginalis. In addition, blood was also collected from the mare and the stallion to check for blood compatibility. Conclusion: Thus, the case was diagnosed as suspected neonatal isoerythrolysis with concurrent Actinomyces hyovaginalis infection
Prevalence of Tidal Interactions among Local Seyfert Galaxies: The Control Experiment
We test whether there is a relation between the observed tidal interactions
and Seyfert activity by imaging in HI twenty inactive galaxies at the same
spatial resolution and detection threshold as the Seyfert sample. This control
sample of inactive galaxies were closely matched in Hubble type, range in size
and inclination, and have roughly comparable galaxy optical luminosity to the
Seyfert galaxies. We find that only ~15% of the galaxies in our control sample
are disturbed in HI, whereas the remaining ~85% show no disturbances whatsoever
in HI. Even at a spatial resolution of ~10 kpc, none of the latter galaxies
show appreciable HI disturbances reminiscent of tidal features.
In a companion paper (Kuo et al. 2008), we report results from the first
systematic imaging survey of Seyfert galaxies in atomic hydrogen (HI) gas. We
find that only ~28% of the eighteen Seyfert galaxies in that sample are visibly
disturbed in optical starlight. By contrast, ~94% of the same Seyfert galaxies
are disturbed spatially and usually also kinematically in HI gas on galactic
scales of >~20 kpc. In at least ~67% and up to perhaps ~94% of cases, the
observed disturbances can be traced to tidal interactions with neighboring
galaxies detected also in HI. The dramatic contrast between the observed
prevalence of HI disturbances in the Seyfert and control samples implicates
tidal interactions in initiating events that lead to luminous Seyfert activity
in a large fraction of local disk galaxies.Comment: 38 pages, 27 figures, Accepted for publication in ApJ. Changes from
previous version: The title of the previous version of this paper appeared in
Astroph was incorrect. It has been replaced with the correct on
马来西亚大学华语二语教材的编写方向 (the direction of TCSL materials in Malaysian Universities)
(abstract only available in Chinese) 学习华语就要有教材,现时的趋势是很多傜来西亚儈等学府的华语课程教材䜭是自编的,很多儈等学府的华语二语讲师䜭很努力地自编和本土化他们的华语课程教材。在这电子媒体盛行,讲求认证和新冠疫情肆虐的时代,为䝽合时代的变迁和新挑战,华语课程新教材也要和汉语水平考试接轨和䝽合电子学习的时代,有些原则上调整,因此教材编写会出现了一些格式和编写上的改变。傜来西亚的华语教学课本的编写历史并不䮯,本土编写的有关课本也不多。开始时,课本模拟中国的对外汉语教学课本来编写,发展到最后才开始有自己的格调,也本地化和根据这䟼的要求来编写。 这篇文章会简单介绍大学的华语教材、和教材有关的教学法、华语文教材编写原则和华语
二语(对外汉语)教材编写原则,过后以编写玛拉工艺大学文凭课程课本生活华语(二)为例提出编写新时代教材的方向,并将过程中会䙷上的䳮仈和解决方案写出来,以为对编写教材有兴趣者提供资料和借鉴
- …