2,001 research outputs found
Finite size effects on calorimetric cooperativity of two-state proteins
Finite size effects on the calorimetric cooperatity of the folding-unfolding
transition in two-state proteins are considered using the Go lattice models
with and without side chains. We show that for models without side chains a
dimensionless measure of calorimetric cooperativity kappa2 defined as the ratio
of the van't Hoff to calorimetric enthalpy does not depend on the number of
amino acids N. The average value of kappa2 is about 3/4 which is lower than the
experimental value kappa2=1. For models with side chains kappa2 approaches
unity as kappa2 \sim N^mu, where exponent mu=0.17. Above the critical chain
length Nc =135 these models can mimic the truly all-or-non folding-unfolding
transition.Comment: 3 eps figures. To appear in the special issue of Physica
Wireless Energy Harvesting Assisted Two-Way Cognitive Relay Networks: Protocol Design and Performance Analysis
This paper analyzes the effects of realistic relay transceiver on the outage probability and throughput of a two-way relay cognitive network that is equipped with an energy-harvesting relay. In this paper, we configure the network with two wireless power transfer policies and two bidirectional relaying protocols. Furthermore, the differences in receiver structure of relay node that can be time switching or power splitting structure are also considered to develop closed-form expressions of outage and throughput of the network providing that the delay of transmission is limited. Numerical results are presented to corroborate our analysis for all considered network configurations. This paper facilitates us not only to quantify the degradation of outage probability and throughput due to the impairments of realistic transceiver but also to provide an insight into practical effects of specified configuration of power transfer policy, relaying protocol, and receiver structure on outage and throughput. For instance, the system with multiple access broadcast protocol and the power splitting-based receiver architecture achieves ceiling throughout higher than that of the transmission rate of source nodes. On the contrary, a combination of dual-source energy transfer policy and the time division broadcast protocol is contributed the highest level of limiting factor in terms of transceiver hardware impairments on the network throughput.</p
Correlating low energy impact damage with changes in modal parameters: a preliminary study on composite beams
This paper is an experimental study of the effects of multi-site damage on the vibration response of a composite beam damaged by low energy impact. The variation of the modal parameters with different levels of impact energy and density of impact is studied. Specimens are impacted symmetrically in order to induce a global rate of damage. A damage detection tool Damage Index is introduced in order to verify the estimation of damping ratios. Design of Experiments is used to establish the sensitivity of both energy of impact and density of damage. The DOE analysis results (using natural frequency only) indicate that impact energy for 2nd, 3rd and 4th bending modes is the most significant factor contributing to the changes in the modal parameters for this kind of symmetrical dynamic test
Reversible stretching of homopolymers and random heteropolymers
We have analyzed the equilibrium response of chain molecules to stretching.
For a homogeneous sequence of monomers, the induced transition from compact
globule to extended coil below the -temperature is predicted to be
sharp. For random sequences, however, the transition may be smoothed by a
prevalence of necklace-like structures, in which globular regions and coil
regions coexist in a single chain. As we show in the context of a random
copolymer, preferential solvation of one monomer type lends stability to such
structures. The range of stretching forces over which necklaces are stable is
sensitive to chain length as well as sequence statistics.Comment: 14 pages, 4 figure
System-level investigation of multi-MW direct-drive wind power PM vernier generators
Surface mounted permanent magnet Vernier (SPM-V) machines are known for their high torque density but relatively poor power factor compared to conventional SPM machines. The high torque density feature of the SPM-V machines is desirable for direct-drive offshore wind power applications as it leads to reduced generator size, mass and cost. However, their poor power factor can negatively affect the converter cost and efficiency. This paper compares the system-level performance, including generator active and structural components and converter, between the SPM-V and the conventional SPM generator systems. Four different power ratings, i.e. 0.5MW, 3MW, 5MW and 10MW, have been considered to study the trend of system-level performance with increasing power rating. The study shows that the SPM-V generators can be lighter and cheaper than their conventional SPM counterparts. However, after the consideration of converter cost and efficiency, the conventional SPM generator exhibited slightly better overall performance. Nonetheless, with the development of novel Vernier topologies and reduction in converter costs in the future due to emerging technologies, the Vernier generators can still be competitive for direct-drive offshore wind power applications
Photon interferometry and size of the hot zone in relativistic heavy ion collisions
The parameters obtained from the theoretical analysis of the single photon
spectra observed by the WA98 collaboration at SPS energies have been used to
evaluate the two photon correlation functions. The single photon spectra and
the two photon correlations at RHIC energies have also been evaluated, taking
into account the effects of the possible spectral change of hadrons in a
thermal bath. We find that the ratio for SPS and
for RHIC energy.Comment: text changed, figures adde
Rigorous analysis of extremely asymmetrical scattering of electromagnetic waves in slanted periodic gratings
Extremely asymmetrical scattering (EAS) is a new type of Bragg scattering in
thick, slanted, periodic gratings. It is realised when the scattered wave
propagates parallel to the front boundary of the grating. Its most important
feature is the strong resonant increase in the scattered wave amplitude
compared to the amplitude of the incident wave: the smaller the grating
amplitude, the larger the amplitude of the scattered wave. In this paper,
rigorous numerical analysis of EAS is carried out by means of the enhanced
T-matrix algorithm. This includes investigation of harmonic generation inside
and outside the grating, unusually strong edge effects, fast oscillations of
the incident wave amplitude in the grating, etc. Comparison with the previously
developed approximate theory is carried out. In particular, it is demonstrated
that the applicability conditions for the two-wave approximation in the case of
EAS are noticeably more restrictive than those for the conventional Bragg
scattering. At the same time, it is shown that the approximate theory is
usually highly accurate in terms of description of EAS in the most interesting
cases of scattering with strong resonant increase of the scattered wave
amplitude. Physical explanation of the predicted effects is presented.Comment: 14 pages, 7 figures; v2: corrections to metadata and bibliographical
info in preprin
Doping dependence of the resonance peak and incommensuration in high- superconductors
The doping and frequency evolutions of the incommensurate spin response and
the resonance mode are studied based on the scenario of the Fermi surface
topology. We use the slave-boson mean-field approach to the
model and including the antiferromagnetic fluctuation correction in the
random-phase approximation. We find that the equality between the
incommensurability and the hole concentration is reproduced at low frequencies
in the underdoped regime. This equality observed in experiments was explained
{\it only} based on the stripe model before. We also obtain the downward
dispersion for the spin response and predict its doping dependence for further
experimental testing, as well as a proportionality between the low-energy
incommensurability and the resonance energy. Our results suggest a common
origin for the incommensuration and the resonance peak based on the Fermi
surface topology and the d-wave symmetry.Comment: 5 pages, 4 PS figure
The use of small angle neutron scattering with contrast matching and variable adsorbate partial pressures in the study of porosity in activated carbons
The porosity of a typical activated carbon is investigated with small angle neutron scattering (SANS), using the contrast matching technique, by changing the hydrogen/deuterium content of the absorbed liquid (toluene) to extract the carbon density at different scattering vector (Q) values and by measuring the p/p0 dependence of the SANS, using fully deuterated toluene. The contrast matching data shows that the apparent density is Q-dependent, either because of pores opening near the carbon surface during the activation processor or changes in D-toluene density in nanoscale pores. For each p/p0 value, evaluation of the Porod Invariant yields the fraction of empty pores. Hence, comparison with the adsorption isotherm shows that the fully dry powder undergoes densification when liquid is added. An algebraic function is developed to fit the SANS signal at each p/p0 value hence yielding the effective Kelvin radii of the liquid surfaces as a function of p/p0. These values, when compared with the Kelvin Equation, show that the resultant surface tension value is accurate for the larger pores but tends to increase for small (nanoscale) pores. The resultant pore size distribution is less model-dependent than for the traditional methods of analyzing the adsorption isotherms
DNA hybridization to mismatched templates: a chip study
High-density oligonucleotide arrays are among the most rapidly expanding
technologies in biology today. In the {\sl GeneChip} system, the reconstruction
of the target concentration depends upon the differential signal generated from
hybridizing the target RNA to two nearly identical templates: a perfect match
(PM) and a single mismatch (MM) probe. It has been observed that a large
fraction of MM probes repeatably bind targets better than the PMs, against the
usual expectation from sequence-specific hybridization; this is difficult to
interpret in terms of the underlying physics. We examine this problem via a
statistical analysis of a large set of microarray experiments. We classify the
probes according to their signal to noise () ratio, defined as the
eccentricity of a (PM, MM) pair's `trajectory' across many experiments. Of
those probes having large () only a fraction behave consistently with
the commonly assumed hybridization model. Our results imply that the physics of
DNA hybridization in microarrays is more complex than expected, and they
suggest new ways of constructing estimators for the target RNA concentration.Comment: 3 figures 1 tabl
- …