On the electrical double layer contribution to the interfacial tension of protein crystals

We study the electrical double layer at the interface between a protein crystal and a salt solution or a dilute solution of protein, and estimate the double layer's contribution to the interfacial tension of this interface. This contribution is negative and decreases in magnitude with increasing salt concentration. We also consider briefly the interaction between a pair of protein surfaces.Comment: 6 pages, 3 figures, revtex

The power of VNA-driven quasi-optics to sense group molecular action in condensed phase systems

© © 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The authors would like to thank the Engineering and Physical Sciences Research Council (EPSRC, UK) for generous support (EP/1014845)

Accurate determination of terahertz optical constants by vector network analyzer of Fabry-Perot response

This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OL.38.005438. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.We present a method based on a Fabry-Perot model to efficiently and accurately estimate optical constants of wafer samples in transmission-only measurements performed by a vector network analyzer (VNA). The method is demonstrated on two separate wafer samples: one of silicon and the other of polymethylmethacrylate. Results show that the method can not only acquire optical constants accurately and simply over a broad frequency domain but also overcome the limitations of calculation for dispersive and lossy materials to which existing methods are susceptible, such as those based on VNA-driven quasi-optical transmissometers and terahertz time-domain spectrometry

Electroneutrality and Phase Behavior of Colloidal Suspensions

Several statistical mechanical theories predict that colloidal suspensions of highly charged macroions and monovalent microions can exhibit unusual thermodynamic phase behavior when strongly deionized. Density-functional, extended Debye-H\"uckel, and response theories, within mean-field and linearization approximations, predict a spinodal phase instability of charged colloids below a critical salt concentration. Poisson-Boltzmann cell model studies of suspensions in Donnan equilibrium with a salt reservoir demonstrate that effective interactions and osmotic pressures predicted by such theories can be sensitive to the choice of reference system, e.g., whether the microion density profiles are expanded about the average potential of the suspension or about the reservoir potential. By unifying Poisson-Boltzmann and response theories within a common perturbative framework, it is shown here that the choice of reference system is dictated by the constraint of global electroneutrality. On this basis, bulk suspensions are best modeled by density-dependent effective interactions derived from a closed reference system in which the counterions are confined to the same volume as the macroions. Linearized theories then predict bulk phase separation of deionized suspensions only when expanded about a physically consistent (closed) reference system. Lower-dimensional systems (e.g., monolayers, small clusters), depending on the strength of macroion-counterion correlations, may be governed instead by density-independent effective interactions tied to an open reference system with counterions dispersed throughout the reservoir, possibly explaining observed structural crossover in colloidal monolayers and anomalous metastability of colloidal crystallites.Comment: 12 pages, 5 figures. Discussion clarified, references adde

Chotuna and Chornancap: Excavating an Ancient Peruvian Legend

Christopher Donnan's Chotuna and Chornancap: Excavating an Ancient Peruvian Legend, explores one of the most intriguing oral histories passed down among ancient Peruvians: the legend of Naymlap, the founder of a dynasty that ruled the Lambayeque Valley of northern Peru centuries before European contact. Naymlap is said to have built his palace at a place that many now consider to be the archaeological sites of Chotuna and Chornancap. In an effort to test the validity of the Naymlap legend, Donnan directed extensive archaeological excavations at Chotuna and Chornancap--completing plans of the monumental architecture, mapping and excavating most of the major structures, and developing a chronology for the sites. This book presents the results of these excavations and demonstrates the extent to which the archaeological evidence correlates with the sequence of events described in the Naymlap legend.Series: Monographs 7

The Effects of Mastication On Memory and Recall in Elementary Students

The purpose of this study was to research the effect of mastication through gum chewing on memory and recall in elementary students. It is imperative to research ways in which to increase brain stimulation in order to enhance memory and recall to provide students with academic success. This research was conducted to assist educators in aiding students in review and recall. Fifty students were randomly selected from first, second, and third grade classrooms in a public school. The students were from varied socioeconomic and intellectual backgrounds with varied family structures. The controlled group of twenty-five students were administered four tests targeting memory and recall. The experimental group of twenty-five participants were administered identical examinations of those in the controlled group. However, the experimental group was given a piece of sugar-free gum to chew during the four sessions. The results of this research indicated that the act of mastication through gum chewing increased students\u27 scores on tests of memory and recall. Mastication improved students\u27 short-term memory when recalling letters and improved auditory memory when memorizing a list of words. The greatest impact of mastication during memory and recall in this project occurred in the trial that tested the memorization of spatial locations. Students who chewed gum during these sessions completed the activity with a quicker speed and memorization