Interaction of laser generated ultrasonic waves with wedge-shaped samples

Wedge-shaped samples can be used as a model of acoustic interactions with samples ranging from ocean wedges, to angled defects such as rolling contact fatigue, to thickness measurements of samples with non-parallel faces. We present work on laser generated ultrasonic waves on metal samples; one can measure the dominant Rayleigh-wave mode, but longitudinal and shear waves are also generated. We present calculations, models, and measurements giving the dependence of the arrival times and amplitudes of these modes on the wedge apex angle and the separation of generation and detection points, and hence give a measure of the wedge characteristics

Robust Chauvenet Outlier Rejection

Sigma clipping is commonly used in astronomy for outlier rejection, but the number of standard deviations beyond which one should clip data from a sample ultimately depends on the size of the sample. Chauvenet rejection is one of the oldest, and simplest, ways to account for this, but, like sigma clipping, depends on the sample's mean and standard deviation, neither of which are robust quantities: Both are easily contaminated by the very outliers they are being used to reject. Many, more robust measures of central tendency, and of sample deviation, exist, but each has a tradeoff with precision. Here, we demonstrate that outlier rejection can be both very robust and very precise if decreasingly robust but increasingly precise techniques are applied in sequence. To this end, we present a variation on Chauvenet rejection that we call "robust" Chauvenet rejection (RCR), which uses three decreasingly robust/increasingly precise measures of central tendency, and four decreasingly robust/increasingly precise measures of sample deviation. We show this sequential approach to be very effective for a wide variety of contaminant types, even when a significant -- even dominant -- fraction of the sample is contaminated, and especially when the contaminants are strong. Furthermore, we have developed a bulk-rejection variant, to significantly decrease computing times, and RCR can be applied both to weighted data, and when fitting parameterized models to data. We present aperture photometry in a contaminated, crowded field as an example. RCR may be used by anyone at https://skynet.unc.edu/rcr, and source code is available there as well.Comment: 62 pages, 48 figures, 7 tables, accepted for publication in ApJ

Theoretical X-Ray Absorption Debye-Waller Factors

An approach is presented for theoretical calculations of the Debye-Waller factors in x-ray absorption spectra. These factors are represented in terms of the cumulant expansion up to third order. They account respectively for the net thermal expansion $\sigma^{(1)}(T)$, the mean-square relative displacements $\sigma^2(T)$, and the asymmetry of the pair distribution function $\sigma^{(3)}(T)$. Similarly, we obtain Debye-Waller factors for x-ray and neutron scattering in terms of the mean-square vibrational amplitudes $u^2(T)$. Our method is based on density functional theory calculations of the dynamical matrix, together with an efficient Lanczos algorithm for projected phonon spectra within the quasi-harmonic approximation. Due to anharmonicity in the interatomic forces, the results are highly sensitive to variations in the equilibrium lattice constants, and hence to the choice of exchange-correlation potential. In order to treat this sensitivity, we introduce two prescriptions: one based on the local density approximation, and a second based on a modified generalized gradient approximation. Illustrative results for the leading cumulants are presented for several materials and compared with experiment and with correlated Einstein and Debye models. We also obtain Born-von Karman parameters and corrections due to perpendicular vibrations.Comment: 11 pages, 8 figure

Electromagnetically induced transparency in superconducting quantum circuits : Effects of decoherence, tunneling and multi-level cross-talk

We explore theoretically electromagnetically-induced transparency (EIT) in a superconducting quantum circuit (SQC). The system is a persistent-current flux qubit biased in a $\Lambda$ configuration. Previously [Phys. Rev. Lett. 93, 087003 (2004)], we showed that an ideally-prepared EIT system provides a sensitive means to probe decoherence. Here, we extend this work by exploring the effects of imperfect dark-state preparation and specific decoherence mechanisms (population loss via tunneling, pure dephasing, and incoherent population exchange). We find an initial, rapid population loss from the $\Lambda$ system for an imperfectly prepared dark state. This is followed by a slower population loss due to both the detuning of the microwave fields from the EIT resonance and the existing decoherence mechanisms. We find analytic expressions for the slow loss rate, with coefficients that depend on the particular decoherence mechanisms, thereby providing a means to probe, identify, and quantify various sources of decoherence with EIT. We go beyond the rotating wave approximation to consider how strong microwave fields can induce additional off-resonant transitions in the SQC, and we show how these effects can be mitigated by compensation of the resulting AC Stark shifts

Systematic variation of central mass density slope in early-type galaxies

We study the total density distribution in the central regions ($<\, 1$ effective radius, $R_{\rm e}$) of early-type galaxies (ETGs), using data from the SPIDER survey. We model each galaxy with two components (dark matter halo + stars), exploring different assumptions for the dark matter (DM) halo profile, and leaving stellar mass-to-light ($M_{\rm \star}/L$) ratios as free fitting parameters to the data. For a Navarro et al. (1996) profile, the slope of the total mass profile is non-universal. For the most massive and largest ETGs, the profile is isothermal in the central regions ($\sim R_{\rm e}/2$), while for the low-mass and smallest systems, the profile is steeper than isothermal, with slopes similar to those for a constant-M/L profile. For a concentration-mass relation steeper than that expected from simulations, the correlation of density slope with mass tends to flatten. Our results clearly point to a "non-homology" in the total mass distribution of ETGs, which simulations of galaxy formation suggest may be related to a varying role of dissipation with galaxy mass.Comment: 3 pages, 1 figure, to appear on the refereed Proceeding of the "The Universe of Digital Sky Surveys" conference held at the INAF--OAC, Naples, on 25th-28th november 2014, to be published on Astrophysics and Space Science Proceedings, edited by Longo, Napolitano, Marconi, Paolillo, Iodic

The Unseen Face of E-Business Project Development

The purpose of this paper is intent on identify and analyze the unseen factors of successful or failure of e-business project development. The IT managers must take into account both all costs involved in e-business development and all phases (analysis, design, testing, implementation, maintenance and operation) according to principle of project management for software/systems life cycle development. There are many solutions to exceed these factors of failure among could be counted outsourcing, a good project management, involvement of senior management, a real cost estimation etc.Zadanie pt. „Digitalizacja i udostępnienie w Cyfrowym Repozytorium Uniwersytetu Łódzkiego kolekcji czasopism naukowych wydawanych przez Uniwersytet Łódzki” nr 885/P-DUN/2014 zostało dofinansowane ze środków MNiSW w ramach działalności upowszechniającej nauk

Topological vortex formation in a Bose-Einstein condensate

Vortices were imprinted in a Bose-Einstein condensate using topological phases. Sodium condensates held in a Ioffe-Pritchard magnetic trap were transformed from a non-rotating state to one with quantized circulation by adiabatically inverting the magnetic bias field along the trap axis. Using surface wave spectroscopy, the axial angular momentum per particle of the vortex states was found to be consistent with $2\hbar$ or $4\hbar$, depending on the hyperfine state of the condensate.Comment: 5 pages, 3 figure

A Revised Model for the Formation of Disk Galaxies: Low Spin and Dark-Halo Expansion

We use observed rotation velocity-luminosity (VL) and size-luminosity (RL) relations to single out a specific scenario for disk galaxy formation in the LCDM cosmology. Our model involves four independent log-normal random variables: dark-halo concentration c, disk spin lam_gal, disk mass fraction m_gal, and stellar mass-to-light ratio M/L_I. A simultaneous match of the VL and RL zero points with adiabatic contraction requires low-c halos, but this model has V_2.2~1.8 V_vir (where V_2.2 and V_vir are the circular velocity at 2.2 disk scale lengths and the virial radius, respectively) which will be unable to match the luminosity function (LF). Similarly models without adiabatic contraction but standard c also predict high values of V_2.2/V_vir. Models in which disk formation induces an expansion rather than the commonly assumed contraction of the dark-matter halos have V_2.2~1.2 V_vir which allows a simultaneous fit of the LF. This may result from non-spherical, clumpy gas accretion, where dynamical friction transfers energy from the gas to the dark matter. This model requires low lam_gal and m_gal values, contrary to naive expectations. However, the low lam_gal is consistent with the notion that disk galaxies predominantly survive in halos with a quiet merger history, while a low m_gal is also indicated by galaxy-galaxy lensing. The smaller than expected scatter in the RL relation, and the lack of correlation between the residuals of the VL and RL relations, respectively, imply that the scatter in lam_gal and in c need to be smaller than predicted for LCDM halos, again consistent with the idea that disk galaxies preferentially reside in halos with a quiet merger history.Comment: 28 pages, 16 figures, ApJ accepted, minor changes from unpublished version, uses emulateapj.cls, high-resolution version available at http://www.ucolick.org/~dutton/65200/hi-res-version/ms.dutton.v2_hr.p