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"Allender, David"
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Shake my sillies out
Animals and campers join together in the woods one evening and shake their sillies, clap their crazies, and yawn their sleepies out.
Book
Recent Experiments Support a Microemulsion Origin of Plasma Membrane Domains: Dependence of Domain Size on Physical Parameters
It is widely, but not universally, believed that the lipids of the plasma membrane are not uniformly distributed, but that “rafts” of sphingolipids and cholesterol float in a “sea” of unsaturated lipids. The physical origin of such heterogeneities is often attributed to a phase coexistence between the two different domains. We argue that this explanation is untenable for several reasons. Further, we note that the results of recent experiments are inconsistent with this picture. However, they are quite consistent with an alternate explanation, namely, that the plasma membrane is a microemulsion of the two kinds of regions. To show this, we briefly review a simplified version of this theory and its phase diagram. We also explicate the dependence of the predicted domain size on four physical parameters. They are the energy cost of gradients in the composition, the spontaneous curvature of the membrane, its bending modulus and its surface tension. Taking values of the latter two from experiment, we obtain domain sizes for several different cell types that vary from 58 to 88 nm.
Journal Article
Model Plasma Membrane exhibits a Microemulsion in both Leaves providing a Foundation for \Rafts\
We consider a model plasma membrane, one that describes the outer leaf as consisting of sphingomyelin, phosphatidylcholine, and cholesterol, and the inner leaf of phosphatidylethanolamine, phosphatidylserine, phosphatidylcholine, and cholesterol. Their relative compositions are taken from experiment, and the cholesterol freely interchanges between leaves. Fluctuations in composition are coupled to fluctuations in the membrane height as in the Leibler-Andelman mechanism. Provided that the membrane is of relatively constant thickness, this coupling of fluctuations also provides a coupling between the composition fluctuations of the two leaves. Structure functions display, for components in both leaves, a peak at non-zero wavevector. This indicates that the disordered fluid membrane is characterized by structure on a scale given by membrane properties. From measurements on the plasma membrane, this scale is on the order of 100 nm. The theory provides a tenable basis for the origin of \"rafts\".
Paper
Landau theory-based estimates for viscosity coefficients of uniaxial and biaxial nematic liquid crystals
Using Landau theory, it is shown that eight phenomenological parameters are needed to describe and distinguish the twelve viscosity coefficients of a biaxial nematic phase, or the five viscosity coefficients of a uniaxial nematic phase. The dependence of the coefficients on the macroscopic uniaxial and biaxial order parameters is established. Since these order parameters are determined by the anisotropies of the dielectric constant, we show that it should be possible to determine values for all eight of the phenomenological parameters of the theory from measurements of the temperature dependence of the five viscosities of a uniaxial phase.
Paper
Theory of Polar Blue Phases
In liquid crystals, if flexoelectric couplings between polar order and director gradients are strong enough, the uniform nematic phase can become unstable to formation of a modulated polar phase. Previous theories have predicted two types of modulation, twist-bend and splay-bend; the twist-bend phase has been found in recent experiments. Here, we investigate other types of modulation, using lattice simulations and Landau theory. In addition to twist-bend and splay-bend, we also find polar blue phases, with 2D or 3D modulations of both director and polar order. We compare polar blue phases with chiral blue phases, and discuss opportunities for observing them experimentally.
Paper
Landau-deGennes Theory of Biaxial Nematics Re-examined
Recent experiments report that the long looked for thermotropic biaxial nematic phase has been finally detected in some thermotropic liquid crystalline systems. Inspired by these experimental observations we concentrate on some elementary theoretical issues concerned with the classical sixth-order Landau-deGennes free energy expansion in terms of the symmetric and traceless tensor order parameter \\(Q_{\\alpha\\beta}\\). In particular, we fully explore the stability of the biaxial nematic phase giving analytical solutions for all distinct classes of the phase diagrams that theory allows. This includes diagrams with triple- and (tri-)critical points and with multiple (reentrant) biaxial- and uniaxial phase transitions. A brief comparison with predictions of existing molecular theories is also given.
Paper
Child abductions: nightmares in progress
In 1980, Congress passed the Parental Kidnapping Prevention Act3 to strengthen the UCCJA and allowed states to use the Federal Parent Locator Service to obtain address information on noncustodial parents who abducted their children. Congress recognized this and, in 1988, ratified the Hague Convention treaty on missing children with the passage of the International Child Abduction Remedies Act,7 whereby the U.S. Department of State would become involved in noncustodial parental abductions where the abducting parent takes the victim outside the boundaries of the United States.\\n16 Once the felony warrant is on file and if investigators believe the suspect has fled their jurisdiction, the FBI can help obtain a warrant for unlawful flight to avoid prosecution.
Magazine Article
Offender reentry: a returning or reformed criminal?
Perhaps the most vexing problem facing the criminal justice system in the US today is how to deal with offenders who have \"paid their debt to society\" and are released from a structured correctional setting back into the community. Rarely does society lock up a person and \"throw away the key.\" Here, Allender discusses the American criminal justice system and penology in connection to the social implications of offender reentry into the society.
Magazine Article
Community policing: exploring the philosophy
The policy of community policing states that successful programs require the formation of a partnership between the police and area residents. Problem solving represents an important component of the effort. Although criminal activity may mutate and continue, a successful community policing program will help formulate new solutions for new problems. Allender tells more as he explores the philosophy of community policing.
Magazine Article
Confronting Gangs: Crime and the Community
\"Confronting Gangs: Crime and the Community\" by G. David Curry and Scott H. Decker is reviewed.
Book Review