15,099 research outputs found
Scattering of charge carriers by point defects in bilayer graphene
Theory of scattering of massive chiral fermions in bilayer graphene by radial
symmetric potential is developed. It is shown that in the case when the
electron wavelength is much larger than the radius of the potential the
scattering cross-section is proportional to the electron wavelength. This leads
to the mobility independent on the electron concentration. In contrast with the
case of single-layer, neutral and charged defects are, in general, equally
relevant for the resistivity of the bilayer graphene.Comment: final versio
Surface roughness and interfacial slip boundary condition for quartz crystal microbalances
The response of a quartz crystal microbalance (QCM) is considered using a wave equation for the substrate and the Navier-Stokes equations for a finite liquid layer under a slip boundary condition. It is shown that when the slip length to shear wave penetration depth is small, the first order effect of slip is only present in the frequency response. Importantly, in this approximation the frequency response satisfies an additivity relation with a net response equal to a Kanazawa liquid term plus an additional Sauerbrey "rigid" liquid mass. For the slip length to result in an enhanced frequency decrease compared to a no-slip boundary condition, it is shown that the slip length must be negative so that the slip plane is located on the liquid side of the interface. It is argued that the physical application of such a negative slip length could be to the liquid phase response of a QCM with a completely wetted rough surface. Effectively, the model recovers the starting assumption of additivity used in the trapped mass model for the liquid phase response of a QCM having a rough surface. When applying the slip boundary condition to the rough surface problem, slip is not at a molecular level, but is a formal hydrodynamic boundary condition which relates the response of the QCM to that expected from a QCM with a smooth surface. Finally, possible interpretations of the results in terms of acoustic reflectivity are developed and the potential limitations of the additivity result should vapour trapping occur are discussed
Senior olympians' achievement goals and motivational responses
Journal ArticleThe purpose of this study was to examine the motivational perspectives of athletes participating in the Senior Olympic Games. One hundred thirty-seven senior athletes (54 males, 82 females, and 1 nonidentifier) completed measures of goal orientations, beliefs about the causes of success in sport, intrinsic motivation, and views about the purpose of sport. Multivariate analysis revealed a positive association between task orientation and intrinsic motivation, the belief that success in sport is achieved through hard work, and self-improvement-based purposes of sport. In contrast, ego orientation was associated with the belief that success in sport is achieved by those who are gifted with natural ability and who know how to maximize external and deceptive factors. Further, ego orientation was linked to the belief that the purpose of sport was for personal gain. The motivational implications of the present findings are discussed based on the tenets of goal perspective theor
Nitrification-denitrification in WSP: a mechanism for permanent nitrogen removal in maturation ponds
A pilot-scale primary maturation pond was spiked with 15N-labelled ammonia (15NH4Cl) and 15N labelled nitrite (Na15NO2), in order to improve current understanding of the dynamics of inorganic nitrogen transformations and removal in WSP systems. Stable isotope analysis of δ15N showed that
nitrification could be considered as an intermediate step in WSP, which is masked by simultaneous denitrification, under conditions of low algal activity. Molecular microbiology analysis showed that denitrification can be considered a feasible mechanism for permanent nitrogen removal in WSP, which may be supported either by ammonia-oxidising bacteria (AOB) or by methanotrophs, in addition to nitrite-oxidising bacteria (NOB). However, the relative supremacy of the denitrification process over other nitrogen removal mechanisms (e.g., biological uptake) depends upon phytoplanktonic activity
Connection between effective-range expansion and nuclear vertex constant or asymptotic normalization coefficient
Explicit relations between the effective-range expansion and the nuclear
vertex constant or asymptotic normalization coefficient (ANC) for the virtual
decay are derived for an arbitrary orbital momentum together with
the corresponding location condition for the () bound-state energy. They
are valid both for the charged case and for the neutral case. Combining these
relations with the standard effective-range function up to order six makes it
possible to reduce to two the number of free effective-range parameters if an
ANC value is known from experiment. Values for the scattering length, effective
range, and form parameter are determined in this way for the O+,
and He collisions in partial waves where a bound state
exists by using available ANCs deduced from experiments. The resulting
effective-range expansions for these collisions are valid up to energies larger
5 MeV.Comment: 17 pages, 6 figure
The potential therapeutic effects of creatine supplementation on body composition and muscle function in cancer
Low muscle mass in individuals with cancer has a profound impact on quality of life and independence and is associated with greater treatment toxicity and poorer prognosis. Exercise interventions are regularly being investigated as a means to ameliorate treatment-related adverse effects, and nutritional/supplementation strategies to augment adaptations to exercise are highly valuable. Creatine (Cr) is a naturally-occurring substance in the human body that plays a critical role in energy provision during muscle contraction. Given the beneficial effects of Cr supplementation on lean body mass, strength, and physical function in a variety of clinical populations, there is therapeutic potential in individuals with cancer at heightened risk for muscle loss. Here, we provide an overview of Cr physiology, summarize the evidence on the use of Cr supplementation in various aging/clinical populations, explore mechanisms of action, and provide perspectives on the potential therapeutic role of Cr in the exercise oncology setting
Generalized Mean Field Approach to a Resonant Bose-Fermi Mixture
We formulate a generalized mean-field theory of a mixture of fermionic and
bosonic atoms, in which the fermion-boson interaction can be controlled by a
Feshbach resonance. The theory correctly accounts for molecular binding
energies of the molecules in the two-body limit, in contrast to the most
straightforward mean-field theory. Using this theory, we discuss the
equilibrium properties of fermionic molecules created from atom pairs in the
gas. We also address the formation of molecules when the magnetic field is
ramped across the resonance, and present a simple Landau-Zener result for this
process.Comment: 35 page
The absolute position of a resonance peak
It is common practice in scattering theory to correlate between the position
of a resonance peak in the cross section and the real part of a complex energy
of a pole of the scattering amplitude. In this work we show that the resonance
peak position appears at the absolute value of the pole's complex energy rather
than its real part. We further demonstrate that a local theory of resonances
can still be used even in cases previously thought impossible
Quantum Drag Forces on a Sphere Moving Through a Rarefied Gas
As an application of quantum fluid mechanics, we consider the drag force
exerted on a sphere by an ultra-dilute gas. Quantum mechanical diffraction
scattering theory enters in that regime wherein the mean free path of a
molecule in the gas is large compared with the sphere radius. The drag force is
computed in a model specified by the ``sticking fraction'' of events in which a
gaseous molecule is adsorbed by the spherical surface. Classical inelastic
scattering theory is shown to be inadequate for physically reasonable sticking
fraction values. The quantum mechanical scattering drag force is exhibited
theoretically and compared with experimental data.Comment: 5 pages no figure
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