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Resampling adaptive cloth simulations onto fixed-topology meshes
We describe a method for converting an adaptively remeshed simulation of cloth into an animated mesh with fixed topology. The topology of the mesh may be specified by the user or computed automatically. In the latter case, we present a method for computing the optimal output mesh, that is, a mesh with spatially varying resolution which is fine enough to resolve all the detail present in the animation. This technique allows adaptive simulations to be easily used in applications that expect fixed-topology animated meshes
A Hybrid Computational and Analytical Model of Inline Drip Emitters
This paper details a hybrid computational and analytical model to predict the performance of inline pressure-compensating (PC) drip irrigation emitters. The term inline refers to flow control devices mounted within the irrigation tubing. Pressure-compensating emitters deliver a relatively constant flow rate over a range applied pressure to accurately meter water to crops. Flow rate is controlled within the emitter by directing the water through a tortuous path (which imposes a fixed resistance), and then through a variable resistor composed of a flexible membrane that deflects under changes in pressure, restricting the flow path. An experimentally validated computational fluid dynamics (CFD) model was used to predict flow behavior through tortuous paths, and a pressure resistance parameter was derived to represent the pressure drop with a single variable. The bending and shearing mechanics of the membrane were modeled analytically and refined for accuracy by deriving a correction factor using finite element analysis. A least-squares matrix formulation that calculates the force applied by a line load of any shape, along which there is a prescribed deflection applied on a rectangular membrane, was derived and was found to be accurate to within one percent. The applicability of the assumption of locally fully developed flow through the pressure compensating chamber in a drip emitter was analyzed. The combined hybrid computational-analytical model reduces the computational time of modeling drip emitter performance from days to less than 30 minutes, dramatically lowering the time required to iterate and select optimal designs. The model was validated using three commercially available drip emitters, rated at 1.1, 2, and 3.8 L/hr. For each, the model predicted the flow rate with an error of twenty percent or less, as compared to the emitter performance published by the manufacturer.Jain Irrigation Systems Ltd.National Science Foundation (U.S.). Graduate Research FellowshipMassachusetts Institute of Technology. Tata Center for Technology and Desig
Determination of Resistance Factor for Tortuous Paths in Drip Emitters
Drip irrigation has the potential to decrease water consumption and increase crop yields and profit. Globally, drip irrigation has had low adoption rates. There are several major barriers to adoption, including the cost of the system and its energy consumption. Mathematical models describing the behavior of drip emitters can provide insights on the performance of drip systems. The models and procedures developed in this paper can be used as a tool for the design of improved drip irrigation systems. This paper presents a method of combining a CFD model that characterizes flow through the tortuous paths of emitters with an analytical model describing pressure-compensating behavior. The CFD model detailed in this paper was verified for three commercially available emitter designs. The model fell within acceptable variation bounds when compared to experimental data. The results of CFD analysis are represented in a resistance factor that can be used in a hybrid analyticalcomputational model. This method requires significantly less processing than using computational models alone. Future work on this topic will detail an analytical model that accurately predicts the behavior of inline PC drip emitters of varying geometries and an optimization of the geometry to lower activation pressure and material costs. Analytical models to predict the flow behavior of a range of tortuous path designs given a prescribed geometry will also be developed.Jain Irrigation System Ltd.National Science Foundation (U.S.). Graduate Research Fellowship Progra
Radial Vibration of an Aeolotropic Cylindrical Shell of Varying Density in a Magnetic Field
In this paper, we have discussed the problem of vibration of cylindrical
shell of aelotropic material of variable density for two different cases-
first, when the density varies linearly and second, when it varies inversely
as the radius vecto
Are Coronae of Magnetically Active Stars Heated by Flares? III. Analytical Distribution of Superimposed Flares
(abridged) We study the hypothesis that observed X-ray/extreme ultraviolet
emission from coronae of magnetically active stars is entirely (or to a large
part) due to the superposition of flares, using an analytic approach to
determine the amplitude distribution of flares in light curves. The
flare-heating hypothesis is motivated by time series that show continuous
variability suggesting the presence of a large number of superimposed flares
with similar rise and decay time scales. We rigorously relate the amplitude
distribution of stellar flares to the observed histograms of binned counts and
photon waiting times, under the assumption that the flares occur at random and
have similar shapes. Applying these results to EUVE/DS observations of the
flaring star AD Leo, we find that the flare amplitude distribution can be
represented by a truncated power law with a power law index of 2.3 +/- 0.1. Our
analytical results agree with existing Monte Carlo results of Kashyap et al.
(2002) and Guedel et al. (2003). The method is applicable to a wide range of
further stochastically bursting astrophysical sources such as cataclysmic
variables, Gamma Ray Burst substructures, X-ray binaries, and spatially
resolved observations of solar flares.Comment: accepted for publication in Ap
Building GUTs from strings
We study in detail the structure of Grand Unified Theories derived as the
low-energy limit of orbifold four-dimensional strings. To this aim, new
techniques for building level-two symmetric orbifold theories are presented.
New classes of GUTs in the context of symmetric orbifolds are then constructed.
The method of permutation modding is further explored and SO(10) GUTs with both
or -plets are obtained. SU(5) models are also found through this
method. It is shown that, in the context of symmetric orbifold GUTs,
only a single GUT-Higgs, either a or a , can be present and it always
resides in an order-two untwisted sector. Very restrictive results also hold in
the case of . General properties and selection rules for string GUTs are
described. Some of these selection rules forbid the presence of some particular
GUT-Higgs couplings which are sometimes used in SUSY-GUT model building. Some
semi-realistic string GUT examples are presented and their properties briefly
discussed.Comment: 40 pages, no figures, Late
One Loop Beta Functions in Topologically Massive Gravity
We calculate the running of the three coupling constants in cosmological,
topologically massive 3d gravity. We find that \nu, the dimensionless
coefficient of the Chern-Simons term, has vanishing beta function. The flow of
the cosmological constant and Newton's constant depends on \nu, and for any
positive \nu there exist both a trivial and a nontrivial fixed point.Comment: 44 pages, 16 figure
Asymmetric Non-Abelian Orbifolds and Model Building
The rules for the free fermionic string model construction are extended to
include general non-abelian orbifold constructions that go beyond the real
fermionic approach. This generalization is also applied to the asymmetric
orbifold rules recently introduced. These non-abelian orbifold rules are quite
easy to use. Examples are given to illustrate their applications.Comment: 30 pages, Revtex 3.
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