1,164 research outputs found
Spectroscopic and Photometric Study of the Contact Binary BO CVn
We present the results of the study of the contact binary system BO CVn. We
have obtained physical parameters of the components based on combined analysis
of new, multi-color light curves and spectroscopic mass ratio. This is the
first time the latter has been determined for this object. We derived the
contact configuration for the system with a very high filling factor of about
88 percent. We were able to reproduce the observed light curve, namely the flat
bottom of the secondary minimum, only if a third light has been added into the
list of free parameters. The resulting third light contribution is significant,
about 20-24 percent, while the absolute parameters of components are: M1=1.16,
M2=0.39, R1=1.62 and R2=1.00 (in solar units). The O-C diagram shows an upward
parabola which, under the conservative mass transfer assumption, would
correspond to a mass transfer rate of dM/dt = 6.3 \times 10-8M\odot/yr, matter
being transferred from the less massive component to the more massive one. No
cyclic, short-period variations have been found in the O-C diagram (but
longer-term variations remain a possibility)Comment: 16 pages, 5 figures, 5 tables, accepted for publication by New
Astronom
RZ Comae - A W-Type Overcontact Eclipsing Binary}
RZ Com (GSC 1990-2841) is a short period (P = 0.3385 d) W UMa-type
binary system, type-W, which has had, over the years, two spectroscopic and
numerous light curve studies. The various mass determinations show a large
scatter. Here we present the results of new light curve and radial velocity
observations, and a fresh analysis by the Wilson-Devinney 2003 code. We
have been able to obtain a unified model for photometric five datasets,
each used one or more filters. The main model parameters such as mass ratio,
temperature, potential, and inclination were in close agreement, as
were derived quantities such as mass, stellar radius, etc. Only the spot
parameters differed, as one might expect. Further, we determined a distance
estimate, r = 204 +- 5 pc, in good agreement with the Gaia value of
r = 203.1 +- 3.7 pc. We also presented four new eclipse timings, performed
a renewed period analysis attaining a LiTE fit. With that we
determined a rate of intrinsic period change dP/dt = 3.86(2) x 10^-8
days/year, and - assuming conservative processes - a rate of mass exchange
dm_1/ dt = -4.1(3) x 10^-8 Msun/year which means that the less massive
star is losing mass to its companion
NorKing Russet, A New Potato Variety
This article gives background into the breeding history that lead to the potato variety named Nor King Russet. It resulted from a cross between Nooksack and ND9567-2Russ. Nooksack is a russet variety grown for processing (french fry) in the northwestern states and ND9567-2Russ resulted from a cross between two number selections that have Norchip and B5141-6 in their pedigrees
Period Analysis, Roche Modeling and Absolute Parameters for AU Ser, an Overcontact Binary System
CCD photometric data collected at UnderOak Observatory (UO) and Desert Bloom Observatory (DBO) in three bandpasses (B, V and I_C) produced 10 new times of minimum for AU Ser which were used to revise the linear ephemeris. These results captured in 2011 and 2018 reinforced a longstanding observation that the shape of the light curve from this W UMa binary system (P=0.386497 d) is highly variable. Significantly skewed peaks and differences at maximum light were detected during quadrature which could only be simulated during Roche modeling by positioning a hot spot on the secondary star close to the neck between both constituents. Historically this system has been variously classified as an F8, G5 and K0 system; however, this study supports more recent reports that AU Ser is best described as spectral type K1V-K2V. A fresh assessment of eclipse time residuals over the past 80 years has provided additional insight regarding cyclical changes in orbital period experienced by this interesting variable star
The Formation of Fragments at Corotation in Isothermal Protoplanetary Disks
Numerical hydrodynamics simulations have established that disks which are
evolved under the condition of local isothermality will fragment into small
dense clumps due to gravitational instabilities when the Toomre stability
parameter is sufficiently low. Because fragmentation through disk
instability has been suggested as a gas giant planet formation mechanism, it is
important to understand the physics underlying this process as thoroughly as
possible. In this paper, we offer analytic arguments for why, at low ,
fragments are most likely to form first at the corotation radii of growing
spiral modes, and we support these arguments with results from 3D hydrodynamics
simulations.Comment: 21 pages, 1 figur
Interstitials, Vacancies and Dislocations in Flux-Line Lattices: A Theory of Vortex Crystals, Supersolids and Liquids
We study a three dimensional Abrikosov vortex lattice in the presence of an
equilibrium concentration of vacancy, interstitial and dislocation loops.
Vacancies and interstitials renormalize the long-wavelength bulk and tilt
elastic moduli. Dislocation loops lead to the vanishing of the long-wavelength
shear modulus. The coupling to vacancies and interstitials - which are always
present in the liquid state - allows dislocations to relax stresses by climbing
out of their glide plane. Surprisingly, this mechanism does not yield any
further independent renormalization of the tilt and compressional moduli at
long wavelengths. The long wavelength properties of the resulting state are
formally identical to that of the ``flux-line hexatic'' that is a candidate
``normal'' hexatically ordered vortex liquid state.Comment: 21 RevTeX pgs, 7 eps figures uuencoded; corrected typos, published
versio
Crystallization of a classical two-dimensional electron system: Positional and orientational orders
Crystallization of a classical two-dimensional one-component plasma
(electrons interacting with the Coulomb repulsion in a uniform neutralizing
positive background) is investigated with a molecular dynamics simulation. The
positional and the orientational correlation functions are calculated for the
first time. We have found an indication that the solid phase has a
quasi-long-range (power-law) positional order along with a long-range
orientational order. This indicates that, although the long-range Coulomb
interaction is outside the scope of Mermin's theorem, the absence of ordinary
crystalline order at finite temperatures applies to the electron system as
well. The `hexatic' phase, which is predicted between the liquid and the solid
phases by the Kosterlitz-Thouless-Halperin-Nelson-Young theory, is also
discussed.Comment: 3 pages, 4 figures; Corrected typos; Double columne
Characterization of persistent atrial fibrillation with non‐contact charge density mapping and relationship to voltage
Background
Despite studies using localized high density contact mapping and lower resolution panoramic approaches, the mechanisms that sustain human persistent atrial fibrillation (AF) remain unresolved. Voltage mapping is commonly employed as a surrogate of atrial substrate to guide ablation procedures.
Objective
To study the distribution and temporal stability of activation during persistent AF using a global non-contact charge density approach and compare the findings with bipolar contact mapping.
Methods
Patients undergoing either redo or de novo ablation for persistent AF underwent charge density and voltage mapping to guide the ablation procedure. Offline analysis was performed to measure the temporal stability of three specific charge density activation (CDA) patterns, and the degree of spatial overlap between CDA patterns and low voltage regions.
Results
CDA was observed in patient-specific locations that partially overlapped, comprising local rotational activity (18% of LA), local irregular activity (41% of LA), and focal activity (39% of LA). Local irregular activity had the highest temporal stability. LA voltage was similar in regions with and without CDA.
Conclusion
In persistent AF, CDA patterns appear unrelated to low voltage areas but occur in varying locations with high temporal stability
The role of cardiac MRI in the management of ventricular arrhythmias in ischaemic and non-ischaemic dilated cardiomyopathy
Ventricular tachycardia (VT) and VF account for the majority of sudden cardiac deaths worldwide. Treatments for VT/VF include anti-arrhythmic drugs, ICDs and catheter ablation, but these treatments vary in effectiveness and carry substantial risks and/or expense. Current methods of selecting patients for ICD implantation are imprecise and fail to identify some at-risk patients, while leading to others being overtreated. In this article, the authors discuss the current role and future direction of cardiac MRI (CMRI) in refining diagnosis and personalising ventricular arrhythmia management. The capability of CMRI with gadolinium contrast delayed-enhancement patterns and, more recently, T1 mapping to determine the aetiology of patients presenting with heart failure is well established. Although CMRI imaging in patients with ICDs can be challenging, recent technical developments have started to overcome this. CMRI can contribute to risk stratification, with precise and reproducible assessment of ejection fraction, quantification of scar and ‘border zone’ volumes, and other indices. Detailed tissue characterisation has begun to enable creation of personalised computer models to predict an individual patient’s arrhythmia risk. When patients require VT ablation, a substrate-based approach is frequently employed as haemodynamic instability may limit electrophysiological activation mapping. Beyond accurate localisation of substrate, CMRI could be used to predict the location of re-entrant circuits within the scar to guide ablation
Renormalization approach for quantum-dot structures under strong alternating fields
We develop a renormalization method for calculating the electronic structure
of single and double quantum dots under intense ac fields. The nanostructures
are emulated by lattice models with a clear continuum limit of the
effective-mass and single-particle approximations. The coupling to the ac field
is treated non-perturbatively by means of the Floquet Hamiltonian. The
renormalization approach allows the study of dressed states of the nanoscopic
system with realistic geometries as well arbitrary strong ac fields. We give
examples of a single quantum dot, emphasizing the analysis of the
effective-mass limit for lattice models, and double-dot structures, where we
discuss the limit of the well used two-level approximation.Comment: 6 pages, 7 figure
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