36,920 research outputs found
Diffusion and permeation in binary solutions: Application to\ud protein ultrafiltration
During the ultrafiltration of colloidal solutions the particles can form a porous medium (filter cake) or a diffuse boundary layer (concentration polarization) above the semipermeable membrane depending on the magnitude of the filtration pressure. In order to provide a unified description of these phenomena the present work develops some connections between irreversible thermodynamics and poroelasticity. In particular, Fick’s and Darcy’s laws are shown to provide an equivalent description except in two limiting cases – infinite dilution and infinite rigidity of the solute. A new expression for the generalized Stokes-Einstein equation is also obtained, which incorporates the poroelastic Biot-Willis coefficient accounting for the compressibility of the solvent. The theory is utilized to predict the pressure and concentration profiles during the ultrafiltration of a protein solution. The model captures the formation of a diffuse polarization layer at low pressures and a nearly rigid filter cake at higher pressures, as well as intermediate stages. The predicted Darcy pressure profile across the polarization layer is in good quantitative agreement with experimental measurements
Structure of Fluctuation Terms in the Trace Dynamics Ward Identity
We give a detailed analysis of the anti-self-adjoint operator contribution to
the fluctuation terms in the trace dynamics Ward identity. This clarifies the
origin of the apparent inconsistency between two forms of this identity
discussed in Chapter 6 of our recent book on emergent quantum theory.Comment: TeX; 14 pages. Dedicated to Rafael Sorkin on the occasion of his 60th
birthda
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Real estate portfolio size and risk reduction
The reduction of portfolio risk is important to all investors but is particularly important to real estate investors as most property portfolios are generally small. As a consequence, portfolios are vulnerable to a significant risk of under-performing the market, or a target rate of return and so investors may be exposing themselves to greater risk than necessary. Given the potentially higher risk of underperformance from owning only a few properties, we follow the approach of Vassal (2001) and examine the benefits of holding more properties in a real estate portfolio. Using Monte Carlo simulation and the returns from 1,728 properties in the IPD database, held over the 10-year period from 1995 to 2004, the results show that increases in portfolio size offers the possibility of a more stable and less volatile return pattern over time, i.e. down-side risk is diminished with increasing portfolio size. Nonetheless, increasing portfolio size has the disadvantage of restricting the probability of out-performing the benchmark index by a significant amount. In other words, although increasing portfolio size reduces the down-side risk in a portfolio, it also decreases its up-side potential. Be that as it may, the results provide further evidence that portfolios with large numbers of properties are always preferable to portfolios of a smaller size
A Strategy for a Vanishing Cosmological Constant in the Presence of Scale Invariance Breaking
Recent work has shown that complex quantum field theory emerges as a
statistical mechanical approximation to an underlying noncommutative operator
dynamics based on a total trace action. In this dynamics, scale invariance of
the trace action becomes the statement , with the operator stress energy tensor, and with the trace over the
underlying Hilbert space. We show that this condition implies the vanishing of
the cosmological constant and vacuum energy in the emergent quantum field
theory. However, since the scale invariance condition does not require the
operator to vanish, the spontaneous breakdown of scale
invariance is still permitted.Comment: Second award in the Gravity Research Foundation Essay Competition for
1997; to appear in General Relativity and Gravitation. Plain Tex, no figure
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Non-normal real estate return distributions by property type in the U.K.
Investment risk models with infinite variance provide a better description of distributions of individual property returns in the IPD database over the period 1981 to 2003 than Normally distributed risk models, which mirrors results in the U.S. and Australia using identical methodology. Real estate investment risk is heteroscedastic, but the Characteristic Exponent of the investment risk function is constant across time yet may vary by property type. Asset diversification is far less effective at reducing the impact of non-systematic investment risk on real estate portfolios than in the case of assets with Normally distributed investment risk. Multi-risk factor portfolio allocation models based on measures of investment codependence from finite-variance statistics are ineffectual in the real estate context
Properties of the Charmed P-wave Mesons
Two broad charmed mesons, the D_0^* and D_1', have recently been observed. We
examine the quark model predictions for the D_0^* and D_1' properties and
discuss experimental measurements that can shed light on them. We find that
these states are well described as the broad, j=1/2 non-strange charmed P-wave
mesons. Understanding the D_0^* and D_1' states can provide important insights
into the D_{sJ}^*(2317), D_{sJ}(2460) states whose unexpected properties have
led to renewed interest in hadron spectroscopy.Comment: 7 pages. Some additional discussion and reference
Synthesis of Quantum Logic Circuits
We discuss efficient quantum logic circuits which perform two tasks: (i)
implementing generic quantum computations and (ii) initializing quantum
registers. In contrast to conventional computing, the latter task is nontrivial
because the state-space of an n-qubit register is not finite and contains
exponential superpositions of classical bit strings. Our proposed circuits are
asymptotically optimal for respective tasks and improve published results by at
least a factor of two.
The circuits for generic quantum computation constructed by our algorithms
are the most efficient known today in terms of the number of expensive gates
(quantum controlled-NOTs). They are based on an analogue of the Shannon
decomposition of Boolean functions and a new circuit block, quantum
multiplexor, that generalizes several known constructions. A theoretical lower
bound implies that our circuits cannot be improved by more than a factor of
two. We additionally show how to accommodate the severe architectural
limitation of using only nearest-neighbor gates that is representative of
current implementation technologies. This increases the number of gates by
almost an order of magnitude, but preserves the asymptotic optimality of gate
counts.Comment: 18 pages; v5 fixes minor bugs; v4 is a complete rewrite of v3, with
6x more content, a theory of quantum multiplexors and Quantum Shannon
Decomposition. A key result on generic circuit synthesis has been improved to
~23/48*4^n CNOTs for n qubit
Survival, Development and Population Dynamics of \u3ci\u3eEmpoasca Fabae\u3c/i\u3e (Homoptera: Cicadellidae) on Three Legume Hosts
Survival and development of potato leafhopper, Empoasca fabae, nymphs were measured on alfalfa (Medicago sativa), birdsfoot trefoil (Lotus corniculatus), and red clover (Trifolium pratense). Survival was not significantly different among host plants (mean = 62%). There was no interaction between sex and host plant for developmental time. Males developed significantly faster than females. Developmental time was fastest on alfalfa, intermediate on trefoil, and slowest on red clover. Plots of alfalfa, trefoil, and red clover were planted to compare the seasonal abundance of the potato leafhopper in the three forages. Nymphs were more abundant in trefoil than in alfalfa and red clover late in July, but no differences occurred on the other sample dates. At their peak, adults were more abundant in alfalfa than in trefoil and red clover
Universal monopole scaling near transitions from the Coulomb phase
Certain frustrated systems, including spin ice and dimer models, exhibit a
Coulomb phase at low temperatures, with power-law correlations and
fractionalized monopole excitations. Transitions out of this phase, at which
the effective gauge theory becomes confining, provide examples of
unconventional criticality. This work studies the behavior at nonzero monopole
density near such transitions, using scaling theory to arrive at universal
expressions for the crossover phenomena. For a particular transition in spin
ice, quantitative predictions are made through a duality mapping to the XY
model, and confirmed using Monte Carlo simulations.Comment: 4.5 pages, 4 figure
Phenalene-phosphazene complexes: effect of exocyclic charge densities on the cyclotriphosphazene ring system
The synthesis and properties of a new series of 1,9-diamino-substituted phenalene complexes of the cyclotriphosphazene ring system is described. One of the compounds is shown to be amphoteric, and this behavior allows an examination of the response of the phosphazene linkage to variations in exocyclic charge density at the spiro center in a plane perpendicular to the cyclotriphosphazene ring system. ^(31)P NMR spectroscopy indicates that substituent lone pairs with this orientation are not effective in long-range delocalization within the phosphazene linkage (in accord with our theoretical model of spiro delocalization). An X-ray crystal structure of one compound (7) identifies the presence of clathrated molecules of chloroform together with doubly hydrogen-bonded pairs of the phenalene-phosphazene complexes in the lattice. Crystal data for 7 (C_(13)H_8Cl_4N_5P_3•CHCl_3): monoclinic space group P2_1/c, a = 12.401 (4) Å, b = 28.404 (6) Å, c = 12.962 (3) Å, β = 91.76 (2)°, V = 4564 (2) Å^3, Z = 8, R = 0.050 for 4525 reflections
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