680 research outputs found
Theory for the nonequilibrium dynamics of flexible chain molecules: relaxation to equilibrium of pentadecane from an all-trans conformation
We extend to nonequilibrium processes our recent theory for the long time
dynamics of flexible chain molecules. While the previous theory describes the
equilibrium motions for any bond or interatomic separation in (bio)polymers by
time correlation functions, the present extension of the theory enables the
prediction of the nonequilibrium relaxation that occurs in processes, such as
T-jump experiments, where there are sudden transitions between, for example,
different equilibrium states. As a test of the theory, we consider the
``unfolding'' of pentadecane when it is transported from a constrained
all-trans conformation to a random-coil state at thermal equilibrium. The time
evolution of the mean-square end-to-end distance after release of the
constraint is computed both from the theory and from Brownian dynamics (BD)
simulations. The predictions of the theory agree very well with the BD
simulations. Furthermore, the theory produces enormous savings in computer
time. This work is a starting point for the application of the new method to
nonequilibrium processes with biological importance such as the helix-coil
transition and protein folding.Comment: 11 pages total, including 2 Postscript figures; submitted to Journal
of Chemical Physic
Bulk correlation functions in 2D quantum gravity
We compute bulk 3- and 4-point tachyon correlators in the 2d Liouville
gravity with non-rational matter central charge c<1, following and comparing
two approaches. The continuous CFT approach exploits the action on the tachyons
of the ground ring generators deformed by Liouville and matter ``screening
charges''. A by-product general formula for the matter 3-point OPE structure
constants is derived. We also consider a ``diagonal'' CFT of 2D quantum
gravity, in which the degenerate fields are restricted to the diagonal of the
semi-infinite Kac table. The discrete formulation of the theory is a
generalization of the ADE string theories, in which the target space is the
semi-infinite chain of points.Comment: 14 pages, 2 figure
On Kernel Formulas and Dispersionless Hirota Equations
We rederive dispersionless Hirota equations of the dispersionless Toda
hierarchy from the method of kernel formula provided by Carroll and Kodama. We
then apply the method to derive dispersionless Hirota equations of the extended
dispersionless BKP(EdBKP) hierarchy proposed by Takasaki. Moreover, we verify
associativity equations (WDVV equations) in the EdBKP hierarchy from
dispersionless Hirota equations and give a realization of associative algebra
with structure constants expressed in terms of residue formula.Comment: 30 pages, minor corrections, references adde
High-speed bipolar phototransistors in a 180nm CMOS process
AbstractSeveral high-speed pnp phototransistors built in a standard 180nm CMOS process are presented. The phototransistors were implemented in sizes of 40×40μm2 and 100×100μm2. Different base and emitter areas lead to different characteristics of the phototransistors. As starting material a p+ wafer with a p− epitaxial layer on top was used. The phototransistors were optically characterized at wavelengths of 410, 675 and 850nm. Bandwidths up to 92MHz and dynamic responsivities up to 2.95A/W were achieved. Evaluating the results, we can say that the presented phototransistors are well suited for high speed photosensitive optical applications where inherent amplification is needed. Further on, the standard silicon CMOS implementation opens the possibility for cheap integration of integrated optoelectronic circuits. Possible applications for the presented phototransistors are low cost high speed image sensors, opto-couplers, etc
A Spatial Quantile Regression Hedonic Model of Agricultural Land Prices
Abstract Land price studies typically employ hedonic analysis to identify the impact of land characteristics on price. Owing to the spatial fixity of land, however, the question of possible spatial dependence in agricultural land prices arises. The presence of spatial dependence in agricultural land prices can have serious consequences for the hedonic model analysis. Ignoring spatial autocorrelation can lead to biased estimates in land price hedonic models. We propose using a flexible quantile regression-based estimation of the spatial lag hedonic model allowing for varying effects of the characteristics and, more importantly, varying degrees of spatial autocorrelation. In applying this approach to a sample of agricultural land sales in Northern Ireland we find that the market effectively consists of two relatively separate segments. The larger of these two segments conforms to the conventional hedonic model with no spatial lag dependence, while the smaller, much thinner market segment exhibits considerable spatial lag dependence. Un mod�le h�donique � r�gression quantile spatiale des prix des terrains agricoles R�sum� Les �tudes sur le prix des terrains font g�n�ralement usage d'une analyse h�donique pour identifier l'impact des caract�ristiques des terrains sur le prix. Toutefois, du fait de la fixit� spatiale des terrains, la question d'une �ventuelle d�pendance spatiale sur la valeur des terrains agricoles se pose. L'existence d'une d�pendance spatiale dans le prix des terrains agricoles peut avoir des cons�quences importantes sur l'analyse du mod�le h�donique. En ignorant cette corr�lation s�rielle, on s'expose au risque d'�valuations biais�es des mod�les h�doniques du prix des terrains. Nous proposons l'emploi d'une estimation � base de r�gression flexible du mod�le h�donique � d�calage spatial, tenant compte de diff�rents effets des caract�ristiques, et surtout de diff�rents degr�s de corr�lations s�rielles spatiales. En appliquant ce principe � un �chantillon de ventes de terrains agricoles en Irlande du Nord, nous d�couvrons que le march� se compose de deux segments relativement distincts. Le plus important de ces deux segments est conforme au mod�le h�donique traditionnel, sans d�pendance du d�calage spatial, tandis que le deuxi�me segment du march�, plus petit et beaucoup plus �troit, pr�sente une d�pendance consid�rable du d�calage spatial. Un modelo hed�nico de regresi�n cuantil espacial de los precios del terreno agr�cola Resumen T�picamente, los estudios del precio de la tierra emplean un an�lisis hed�nico para identificar el impacto de las caracter�sticas de la tierra sobre el precio. No obstante, debido a la fijeza espacial de la tierra, surge la cuesti�n de una posible dependencia espacial en los precios del terreno agr�cola. La presencia de dependencia espacial en los precios del terreno agr�cola puede tener consecuencias graves para el modelo de an�lisis hed�nico. Ignorar la autocorrelaci�n espacial puede conducir a estimados parciales en los modelos hed�nicos del precio de la tierra. Proponemos el uso de una valoraci�n basada en una regresi�n cuantil flexible del modelo hed�nico del lapso espacial que tenga en cuenta los diversos efectos de las caracter�sticas y, particularmente, los diversos grados de autocorrelaci�n espacial. Al aplicar este planteamiento a una muestra de ventas de terreno agr�cola en Irlanda del Norte, descubrimos que el mercado consiste efectivamente de dos segmento relativamente separados. El m�s grande de estos dos segmentos se ajusta al modelo hed�nico convencional sin dependencia del lapso espacial, mientras que el segmento m�s peque�o, y mucho m�s fino, muestra una dependencia considerable del lapso espacial.Spatial lag, quantile regression, hedonic model, C13, C14, C21, Q24,
Study of plasma immersion ion implantation into silicon substrate using magnetic mirror geometry
AbstractThe effect of magnetic field enhanced plasma immersion ion implantation (PIII) in silicon substrate has been investigated at low and high pulsed bias voltages. The magnetic field in magnetic bottle configuration was generated by two magnetic coils installed outside the vacuum chamber. The presence of both, electric and magnetic field in PIII creates a system of crossed E×B fields, promoting plasma rotation around the target. The magnetized electrons drifting in crossed E×B fields provide electron-neutral collision. Consequently, the efficient background gas ionization augments the plasma density around the target where a magnetic confinement is achieved. As a result, the ion current density increases, promoting changes in the samples surface properties, especially in the surface roughness and wettability and also an increase of implantation dose and depth
PNP PIN bipolar phototransistors for high-speed applications built in a 180nm CMOS process
AbstractThis work reports on three speed optimized pnp bipolar phototransistors build in a standard 180nm CMOS process using a special starting wafer. The starting wafer consists of a low doped p epitaxial layer on top of the p substrate. This low doped p epitaxial layer leads to a thick space-charge region between base and collector and thus to a high −3dB bandwidth at low collector–emitter voltages. For a further increase of the bandwidth the presented phototransistors were designed with small emitter areas resulting in a small base-emitter capacitance. The three presented phototransistors were implemented in sizes of 40×40μm2 and 100×100μm2. Optical DC and AC measurements at 410nm, 675nm and 850nm were done for phototransistor characterization. Due to the speed optimized design and the layer structure of the phototransistors, bandwidths up to 76.9MHz and dynamic responsivities up to 2.89A/W were achieved. Furthermore simulations of the electric field strength and space-charge regions were done
On the Yang-Lee and Langer singularities in the O(n) loop model
We use the method of `coupling to 2d QG' to study the analytic properties of
the universal specific free energy of the O(n) loop model in complex magnetic
field. We compute the specific free energy on a dynamical lattice using the
correspondence with a matrix model. The free energy has a pair of Yang-Lee
edges on the high-temperature sheet and a Langer type branch cut on the
low-temperature sheet. Our result confirms a conjecture by A. and Al.
Zamolodchikov about the decay rate of the metastable vacuum in presence of
Liouville gravity and gives strong evidence about the existence of a weakly
metastable state and a Langer branch cut in the O(n) loop model on a flat
lattice. Our results are compatible with the Fonseca-Zamolodchikov conjecture
that the Yang-Lee edge appears as the nearest singularity under the Langer cut.Comment: 38 pages, 16 figure
Macroscopoic Three-Loop Amplitudes and the Fusion Rules from the Two-Matrix Model
From the computation of three-point singlet correlators in the two-matrix
model, we obtain an explicit expression for the macroscopic three-loop
amplitudes having boundary lengths in the case of
the unitary series coupled to two-dimensional gravity. The sum
appearing in this expression is found to conform to the structure of the CFT
fusion rules while the summand factorizes through a product of three modified
Bessel functions. We briefly discuss a possible generalization of these
features to macroscopic -loop amplitudes.Comment: 9 pages, no figure, late
Loop Equations for + and - Loops in c = 1/2 Non-Critical String Theory
New loop equations for all genera in non-critical string
theory are constructed. Our loop equations include two types of loops, loops
with all Ising spins up (+ loops) and those with all spins down ( loops).
The loop equations generate an algebra which is a certain extension of
algebra and are equivalent to the constraints derived before in the
matrix-model formulation of 2d gravity. Application of these loop equations to
construction of Hamiltonian for string field theory is
considered.Comment: 21 pages, LaTex file, no figure
- …