10,010 research outputs found
A study of the dynamics of rotating space stations with elastically connected counterweight and attached flexible appendages. Volume 1: Theory
The formulation of a mathematical model for predicting the dynamic behavior of rotating flexible space station configurations was conducted. The overall objectives of the study were: (1) to develop the theoretical techniques for determining the behavior of a realistically modeled rotating space station, (2) to provide a versatile computer program for the numerical analysis, and (3) to present practical concepts for experimental verification of the analytical results. The mathematical model and its associated computer program are described
Gravitational Wave Burst Source Direction Estimation using Time and Amplitude Information
In this article we study two problems that arise when using timing and
amplitude estimates from a network of interferometers (IFOs) to evaluate the
direction of an incident gravitational wave burst (GWB). First, we discuss an
angular bias in the least squares timing-based approach that becomes
increasingly relevant for moderate to low signal-to-noise ratios. We show how
estimates of the arrival time uncertainties in each detector can be used to
correct this bias. We also introduce a stand alone parameter estimation
algorithm that can improve the arrival time estimation and provide
root-sum-squared strain amplitude (hrss) values for each site. In the second
part of the paper we discuss how to resolve the directional ambiguity that
arises from observations in three non co-located interferometers between the
true source location and its mirror image across the plane containing the
detectors. We introduce a new, exact relationship among the hrss values at the
three sites that, for sufficiently large signal amplitudes, determines the true
source direction regardless of whether or not the signal is linearly polarized.
Both the algorithm estimating arrival times, arrival time uncertainties, and
hrss values and the directional follow-up can be applied to any set of
gravitational wave candidates observed in a network of three non co-located
interferometers. As a case study we test the methods on simulated waveforms
embedded in simulations of the noise of the LIGO and Virgo detectors at design
sensitivity.Comment: 10 pages, 14 figures, submitted to PR
Complex X-ray spectral variability in Mkn 421 observed with XMM-Newton
The bright blazar Mkn 421 has been observed four times for uninterrupted
durations of ~ 9 - 13 hr during the performance verification and calibration
phases of the XMM-Newton mission. The source was strongly variable in all
epochs, with variability amplitudes that generally increased to higher energy
bands. Although the detailed relationship between soft (0.1 - 0.75 keV) and
hard (2 - 10 keV) band differed from one epoch to the next, in no case was
there any evidence for a measurable interband lag, with robust upper limits of
hr in the best-correlated light curves. This is in conflict
with previous claims of both hard and soft lags of ~1 hr in this and other
blazars. However, previous observations suffered a repeated 1.6 hr feature
induced by the low-Earth orbital period, a feature that is not present in the
uninterrupted XMM-Newton data. The new upper limit on leads to a lower
limit on the magnetic field strength and Doppler factor of B \delta^{1/3} \gs
4.7 G, mildly out of line with the predictions from a variety of homogeneous
synchrotron self-Compton emission models in the literature of G. Time-dependent spectral fitting was performed on all epochs,
and no detectable spectral hysteresis was seen. We note however that the source
exhibited significantly different spectral evolutionary behavior from one epoch
to the next, with the strongest correlations in the first and last and an
actual divergance between soft and hard X-ray bands in the third. This
indicates that the range of spectral variability behavior in Mkn 421 is not
fully described in these short snippets; significantly longer uninterrupted
light curves are required, and can be obtained with XMM-Newton.Comment: 21 pages, 4 figures, accepted for ApJ, scheduled for August 1, 200
Day 3 - Creative Collaborations II: Workshop on Trust, Communication, and Negotiation
Let’s face it: teamwork can be a real challenge sometimes. Conflicts that arise within a research team can negatively impact the careers of team members and the outcomes of the research itself, so learning to avoid and solve conflicts through trust, communication, and negotiation is key to research team success. In this session, Dr. Monika Markowitz, Director of the Office of Research Integrity and Ethics, and Mark Rubin, Executive Director of the Virginia Center for Consensus Building, will help attendees understand some of the most common research, professional, and interpersonal conflicts that occur in research teams, as well as how to help prevent these conflicts and what to do when they occur. Attendees will see negotiation skills modeled and have the opportunity to practice their own skills as they analyze and respond to example conflicts
Optimal Investment in the Development of Oil and Gas Field
Let an oil and gas field consists of clusters in each of which an investor
can launch at most one project. During the implementation of a particular
project, all characteristics are known, including annual production volumes,
necessary investment volumes, and profit. The total amount of investments that
the investor spends on developing the field during the entire planning period
we know. It is required to determine which projects to implement in each
cluster so that, within the total amount of investments, the profit for the
entire planning period is maximum.
The problem under consideration is NP-hard. However, it is solved by dynamic
programming with pseudopolynomial time complexity. Nevertheless, in practice,
there are additional constraints that do not allow solving the problem with
acceptable accuracy at a reasonable time. Such restrictions, in particular, are
annual production volumes. In this paper, we considered only the upper
constraints that are dictated by the pipeline capacity. For the investment
optimization problem with such additional restrictions, we obtain qualitative
results, propose an approximate algorithm, and investigate its properties.
Based on the results of a numerical experiment, we conclude that the developed
algorithm builds a solution close (in terms of the objective function) to the
optimal one
X-ray Characteristics of NGC 3516: A View through the Complex Absorber
We consider new Suzaku data for NGC 3516 taken during 2009, along with other
recent X-ray observations of the source. The cumulative characteristics of NGC
3516 cannot be explained without invoking changes in the line-of-sight
absorption. Contrary to many other well-studied Seyfert galaxies, NGC 3516 does
not show a positive lag of hard X-ray photons relative to soft photons over the
timescales sampled. In the context of reverberation models for the X-ray lags,
the lack of such a signal in NGC 3516 is consistent with flux variations being
dominated by absorption changes. The lack of any reverberation signal in such a
highly variable source disfavors intrinsic continuum variability in this case.
Instead, the colorless flux variations observed at high flux states for NGC
3516 are suggested to be a consequence of Compton-thick clumps of gas crossing
the line-of-sight.Comment: 12 pages, 6 figures, accepted for publication in The Astrophysical
Journa
On the Lichnerowicz conjecture for CR manifolds with mixed signature
We construct examples of nondegenerate CR manifolds with Levi form of
signature , , which are compact, not locally CR flat, and
admit essential CR vector fields. We also construct an example of a noncompact
nondegenerate CR manifold with signature which is not locally CR flat
and admits an essential CR vector fields. These provide counterexamples to the
analogue of the Lichnerowicz conjecture for CR manifolds with mixed signature.Comment: 7 page
A 100ks XMM-Newton view of the Seyfert 1.8 ESO113-G010. I. Discovery of large X-ray variability and study of the FeKalpha line complex
(Abridged) We present here a long (100ks) XMM-Newton follow-up of the Seyfert
1.8 galaxy ESO113-G010 performed in November 2005, in order to study over a
longer time-scale its main X-ray properties. The source was found in a
higher/softer time-averaged flux state, and timing analysis of this source
reveals strong, rapid variability. The Power Spectral Density (PSD) analysis
indicates (at 95% c.l.) a break at 3.7 x 10^-4 Hz. This cut-off frequency is
comparable to those measured in some other rapidly-variable Seyferts, such as
MCG-6-30-15 and NGC4051. From the mass-luminosity-time-scale, we infer that
M_BH ranges from 4 x 10^6 - 10^7 M_odot and the source is accreting at or close
to the Eddington rate (or even higher). The existing data cannot distinguish
between spectral pivoting of the continuum and a two-component origin for the
spectral softening, primarily because the data do not span a broad enough flux
range. In the case of the two-component model, the fractional offsets measured
in the flux-flux plots increase significantly toward higher energies (similar
to what is observed in MCG-6-30-15) as expected if there exists a constant
reflection component. Contrary to May 2001, no significant highly redshifted
emission line is observed (which might be related to the source flux level),
while two narrow emission lines at about 6.5keV and 7keV are observed. The S/N
is not high enough to establish if the lines are variable or constant. As
already suggested by the 2001 observation, no significant constant narrow
6.4keV FeK line (EW~32eV) is observed, hence excluding any dominant emission
from distant cold matter such as a torus in this Seyfert type 1.8 galaxy.Comment: Accepted for publication in A&A, 10 pages, 11 figures, 2 table
Isopropylphenidate: An Ester Homolog of Methylphenidate with Sustained and Selective Dopaminergic Activity and Reduced Drug Interaction Liability
Objective: The most widely utilized pharmacological treatment of attention-deficit/hyperactivity disorder (ADHD) is the psychostimulant methylphenidate (MPH). Most MPH formulations consist of the racemic mixture of d-threo-(R, R)-MPH and l-threo-(S, S)-MPH isomers. MPH is characterized by its low bioavailability and short half-life (2?3 hours). Additionally, significant inter-individual variability in MPH pharmacokinetics has been consistently documented. Accordingly, efforts have been directed at developing alternatives to MPH as therapeutic agents. A wide range of MPH analogues (dl-α-[2-piperidyl]-phenylacetic acid esters) have been synthesized with the dopamine transporter (DAT) and norepinephrine transporter (NET) as principle neuropharmacological targets. The present study investigated the metabolic profiles and pharmacological activity of the isopropyl ester derivative of MPH, dl-isopropylphenidate (IPH), both in vitro and in vivo. Methods: The synthesis, monoaminergic transporter binding, cellular uptake profiles, and assessment of metabolic hydrolysis and transesterification in the presence of ethanol are described using MPH as a comparator. Additionally, an in vivo assessment of IPH stimulant effects (vs. saline) in rats was performed with locomotor activity as a pharmacodynamic outcome. Results: IPH displayed unique pharmacological characteristics including greater DAT than NET binding and cellular uptake activity, and greater resistance to hydrolysis and transesterification via carboxylesterase 1 relative to MPH. Further, sustained psychostimulant properties offer the prospect of an enhanced duration of action. Conclusions: Our findings are consistent with IPH exhibiting attributes distinguishing it from MPH and warranting further study and development of IPH as a novel psychotherapeutic agent.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140321/1/cap.2013.0074.pd
Collective behavior of stock price movements in an emerging market
To investigate the universality of the structure of interactions in different
markets, we analyze the cross-correlation matrix C of stock price fluctuations
in the National Stock Exchange (NSE) of India. We find that this emerging
market exhibits strong correlations in the movement of stock prices compared to
developed markets, such as the New York Stock Exchange (NYSE). This is shown to
be due to the dominant influence of a common market mode on the stock prices.
By comparison, interactions between related stocks, e.g., those belonging to
the same business sector, are much weaker. This lack of distinct sector
identity in emerging markets is explicitly shown by reconstructing the network
of mutually interacting stocks. Spectral analysis of C for NSE reveals that,
the few largest eigenvalues deviate from the bulk of the spectrum predicted by
random matrix theory, but they are far fewer in number compared to, e.g., NYSE.
We show this to be due to the relative weakness of intra-sector interactions
between stocks, compared to the market mode, by modeling stock price dynamics
with a two-factor model. Our results suggest that the emergence of an internal
structure comprising multiple groups of strongly coupled components is a
signature of market development.Comment: 10 pages, 10 figure
- …