2,402 research outputs found
Permutation patterns and statistics
Let S_n denote the symmetric group of all permutations of the set {1, 2,
...,n} and let S = \cup_{n\ge0} S_n. If Pi is a set of permutations, then we
let Av_n(Pi) be the set of permutations in S_n which avoid every permutation of
Pi in the sense of pattern avoidance. One of the celebrated notions in pattern
theory is that of Wilf-equivalence, where Pi and Pi' are Wilf equivalent if
#Av_n(Pi)=#Av_n(Pi') for all n\ge0. In a recent paper, Sagan and Savage
proposed studying a q-analogue of this concept defined as follows. Suppose
st:S->N is a permutation statistic where N represents the nonnegative integers.
Consider the corresponding generating function, F_n^{st}(Pi;q) = sum_{sigma in
Av_n(Pi)} q^{st sigma}, and call Pi,Pi' st-Wilf equivalent if
F_n^{st}(Pi;q)=F_n^{st}(Pi';q) for all n\ge0. We present the first in-depth
study of this concept for the inv and maj statistics. In particular, we
determine all inv- and maj-Wilf equivalences for any Pi containd in S_3. This
leads us to consider various q-analogues of the Catalan numbers, Fibonacci
numbers, triangular numbers, and powers of two. Our proof techniques use
lattice paths, integer partitions, and Foata's fundamental bijection. We also
answer a question about Mahonian pairs raised in the Sagan-Savage article.Comment: 28 pages, 5 figures, tightened up the exposition, noted that some of
the conjectures have been prove
In vivo nuclear magnetic resonance imaging
A number of physiological changes have been demonstrated in bone, muscle and blood after exposure of humans and animals to microgravity. Determining mechanisms and the development of effective countermeasures for long duration space missions is an important NASA goal. The advent of tomographic nuclear magnetic resonance imaging (NMR or MRI) gives NASA a way to greatly extend early studies of this phenomena in ways not previously possible; NMR is also noninvasive and safe. NMR provides both superb anatomical images for volume assessments of individual organs and quantification of chemical/physical changes induced in the examined tissues. The feasibility of NMR as a tool for human physiological research as it is affected by microgravity is demonstrated. The animal studies employed the rear limb suspended rat as a model of mucle atrophy that results from microgravity. And bedrest of normal male subjects was used to simulate the effects of microgravity on bone and muscle
Nonlinear Outcome of Gravitational Instability in Disks with Realistic Cooling
We consider the nonlinear outcome of gravitational instability in optically
thick disks with a realistic cooling function. We use a numerical model that is
local, razor-thin, and unmagnetized. External illumination is ignored. Cooling
is calculated from a one-zone model using analytic fits to low temperature
Rosseland mean opacities. The model has two parameters: the initial surface
density Sigma_0 and the rotation frequency Omega. We survey the parameter space
and find: (1) The disk fragments when t_c,eff Omega = 1, where t_c,eff is an
effective cooling time defined as the average internal energy of the model
divided by the average cooling rate. This is consistent with earlier results
that used a simplified cooling function. (2) The initial cooling time t_c0 or a
uniform disk with Q = 1 can differ by orders of magnitude from t_c,eff in the
nonlinear outcome. The difference is caused by sharp variations in the opacity
with temperature. The condition t_c0 Omega = 1 therefore does not necessarily
indicate where fragmentation will occur. (3) The largest difference between
t_c,eff and t_c0 is near the opacity gap, where dust is absent and hydrogen is
largely molecular. (4) In the limit of strong illumination the disk is
isothermal; we find that an isothermal version of our model fragments for Q <
1.4. Finally, we discuss some physical processes not included in our model, and
find that most are likely to make disks more susceptible to fragmentation. We
conclude that disks with t_c,eff Omega < 1 do not exist.Comment: 30 pages, 12 figure
Vortices in Thin, Compressible, Unmagnetized Disks
We consider the formation and evolution of vortices in a hydrodynamic
shearing-sheet model. The evolution is done numerically using a version of the
ZEUS code. Consistent with earlier results, an injected vorticity field evolves
into a set of long-lived vortices, each of which has a radial extent comparable
to the local scale height. But we also find that the resulting velocity field
has a positive shear stress, . This effect appears
only at high resolution. The transport, which decays with time as t^-1/2,
arises primarily because the vortices drive compressive motions. This result
suggests a possible mechanism for angular momentum transport in low-ionization
disks, with two important caveats: a mechanism must be found to inject
vorticity into the disk, and the vortices must not decay rapidly due to
three-dimensional instabilities.Comment: 8 pages, 10 figures (high resolution figures available in ApJ
electronic edition
A Titanium Nitride Absorber for Controlling Optical Crosstalk in Horn-Coupled Aluminum LEKID Arrays for Millimeter Wavelengths
We discuss the design and measured performance of a titanium nitride (TiN)
mesh absorber we are developing for controlling optical crosstalk in
horn-coupled lumped-element kinetic inductance detector arrays for
millimeter-wavelengths. This absorber was added to the fused silica
anti-reflection coating attached to previously-characterized, 20-element
prototype arrays of LEKIDs fabricated from thin-film aluminum on silicon
substrates. To test the TiN crosstalk absorber, we compared the measured
response and noise properties of LEKID arrays with and without the TiN mesh.
For this test, the LEKIDs were illuminated with an adjustable, incoherent
electronic millimeter-wave source. Our measurements show that the optical
crosstalk in the LEKID array with the TiN absorber is reduced by 66\% on
average, so the approach is effective and a viable candidate for future
kilo-pixel arrays.Comment: 7 pages, 5 figures, accepted for publication in the Journal of Low
Temperature Physic
MaxEnt power spectrum estimation using the Fourier transform for irregularly sampled data applied to a record of stellar luminosity
The principle of maximum entropy is applied to the spectral analysis of a
data signal with general variance matrix and containing gaps in the record. The
role of the entropic regularizer is to prevent one from overestimating
structure in the spectrum when faced with imperfect data. Several arguments are
presented suggesting that the arbitrary prefactor should not be introduced to
the entropy term. The introduction of that factor is not required when a
continuous Poisson distribution is used for the amplitude coefficients. We
compare the formalism for when the variance of the data is known explicitly to
that for when the variance is known only to lie in some finite range. The
result of including the entropic measure factor is to suggest a spectrum
consistent with the variance of the data which has less structure than that
given by the forward transform. An application of the methodology to example
data is demonstrated.Comment: 15 pages, 13 figures, 1 table, major revision, final version,
Accepted for publication in Astrophysics & Space Scienc
Gender & Sport Related Differences in Electrocardiogram & Pre-Participation Exams (PPE) in College Age Athletes
Background and Purpose: The NCAA requires all college level athletes receive a pre-participation physical exam. However, the pre-participation exams occasionally do not require electrocardiogram screening to help detect cardiac abnormalities. Though electrocardiograms may not be available at all testing’s, using specific markers and finding differences between gender and sport abnormalities could help detect cardiac abnormalities. The purpose of this study was to determine if there were significant differences in resting 12-Lead ECG markers in a group NCAA Div. II collegiate level athletes.
Methods: Four hundred fifty-one college level athlete’s ages 18 to 25 participated in this study. Age, gender, height, weight, BMI, blood pressure and heart rate were measured during a pre-participation exam. Electrocardiogram measurements were gathered by using Mortara X-Scribe™ , Vacumed Turbo Fit 5™, Welch Allyn CardioPerfect™. Twelve-Lead ECGs were categorized by sport and analyzed by the lab director and the attending physician. One-way ANOVA was used to analyze differences in ECG findings in sports. Independent t-test and linear regression were used to analyze differences between male and female outcomes. Significance was set at the 0.05 level.
Results: No significant differences in wave durations were found between male and female athletes. However, P wave amplitude was higher in males (1.50 ± 0.61 mm) than females (1.44 ± .55 mm) (P=0.01). Males had higher resting blood pressures (SBP=123.1 ± 10.9 mmHg) (DBP=73.6 ± 8.1 mmHg) than females (SBP=112.6 ± 9.6 mmHg) (DBP=69.9 ± 7.9 mmHg) (P\u3c0.001). Males also had a higher frequency of arrhythmias, T wave inversions, and 1st degree atrioventricular blocks when compared to females. Similarly, SBP was significantly higher in football compared to all other sports. Relative to ECG parameters cross country athletes showed ECG changes typical for cardiovascular endurance training compared to all other sports including sinus bradycardia, increased RR interval, and leftward axis shift.
Discussion: Although marked differences in 12-lead ECG parameters were not found between sports in this sample, two athletes were sent for further echocardiogram evaluation due to abnormal ECGs, but were subsequently cleared to participate in their sport
Kinetic and Structural Analysis of Substrate Specificity in Two Copper Amine Oxidases from Hansenula polymorpha
The structural underpinnings of enzyme substrate specificity are investigated in a pair of copper amine oxidases (CAOs) from Hansenula polymorpha (HPAO-1 and HPAO-2). The X-ray crystal structure (to 2.0 Ă… resolution) and steady state kinetic data of the second copper amine oxidase (HPAO-2) are presented for comparison to HPAO-1. Despite 34 % sequence identity and superimposable active site residues implicated in catalysis, the enzymes vary considerably in their substrate entry channel. The previously studied CAO, HPAO-1, has a narrow substrate channel. In contrast HPAO-2 has a wide funnel-shaped substrate channel, which also contains a side-chamber. In addition, there are a number of amino acid changes within the channels of HPAO-2 and HPAO-1 that may sterically impact the ability of substrates to form covalent Schiff base catalytic intermediates and to initiate chemistry. These differences can partially explain the greatly different substrate specificities as characterized by kcat/Km value differences: in HPAO-1, the kcat/Km for methylamine is 330-fold greater than for benzylamine, whereas in HPAO-2 it is benzylamine that is the better substrate by 750-fold. In HPAO-2 an inflated Dkcat/Km(methylamine) in relation to Dkcat/Km(benzylamine) indicates that proton abstraction has been impeded more than substrate release. In HPAO-1, Dkcat/Km(S) changes little with the slow substrate, and indicates a similar increase in the energy barriers that control both substrate binding and subsequent catalysis. In neither case is kcat/Km for the second substrate, O2, significantly altered. These results reinforce the modular nature of the active sites of CAOs and show that multiple factors contribute to substrate specificity and catalytic efficiency. In HPAO-1, the enzyme with the smaller substrate binding pocket, both initial substrate binding and proton loss are affected by an increase in substrate size, while in HPAO-2, the enzyme with the larger substrate binding pocket, the rate of proton loss is differentially affected when a phenyl substituent in substrate is reduced to the size of a methyl group
A millimeter-wave kinetic inductance detector camera for long-range imaging through optical obscurants
Millimeter-wave imaging provides a promising option for long-range target detection through optical obscurants such as fog, which often occur in marine environments. Given this motivation, we are currently developing a 150 GHz polarization-sensitive imager using a relatively new type of superconducting pair-breaking detector, the kinetic inductance detector (KID). This imager will be paired with a 1.5 m telescope to obtain an angular resolution of 0.09° over a 3.5° field of view using 3,840 KIDs. We have fully characterized a prototype KID array, which shows excellent performance with noise strongly limited by the irreducible fluctuations from the ambient temperature background. Full-scale KID arrays are now being fabricated and characterized for a planned demonstration in a maritime environment later this year
A cryogenic waveplate rotator for polarimetry at mm and sub-mm wavelengths
Mm and sub-mm waves polarimetry is the new frontier of research in Cosmic
Microwave Background and Interstellar Dust studies. Polarimeters working in the
IR to MM range need to be operated at cryogenic temperatures, to limit the
systematic effects related to the emission of the polarization analyzer. In
this paper we study the effect of the temperature of the different components
of a waveplate polarimeter, and describe a system able to rotate, in a
completely automated way, a birefringent crystal at 4K. We simulate the main
systematic effects related to the temperature and non-ideality of the optical
components in a Stokes polarimeter. To limit these effects, a cryogenic
implementation of the polarimeter is mandatory. In our system, the rotation
produced by a step motor, running at room temperature, is transmitted down to
cryogenic temperatures by means of a long shaft and gears running on custom
cryogenic bearings. Our system is able to rotate, in a completely automated
way, a birefringent crystal at 4K, dissipating only a few mW in the cold
environment. A readout system based on optical fibers allows to control the
rotation of the crystal to better than 0.1{\deg}. This device fulfills the
stringent requirements for operation in cryogenic space experiments, like the
forthcoming PILOT, BOOMERanG and LSPE.Comment: Submitted to Astronomy and Astrophysics. v1: 10 pages, 8 figures. v2:
corrected labels for the bibliographic references (no changes in the
bibliography). v3: revised version. 9 pages, 7 figures. Added a new figure.
Updated with a more realistic simulation for the interstellar dust and with
the latest cryogenic test
- …