Wabash College

To evaluate the impact of actual and perceived similarity on interpersonal attraction, we meta-analyzed 460 effect sizes from 313 laboratory and field investigations. Results indicated that the associations between interpersonal attraction and both actual similarity (r = .47) and perceived similarity (r = .39) were significant and large. The data also indicate that (i) actual similarity was important in no-interaction and short-interaction studies, (ii) there was a significant reduction in the effect size of actual similarity beyond no-interaction studies, and (iii) the effect of actual similarity in existing relationships was not significant. Alternatively, perceived similarity predicted attraction in no-interaction, short-interaction, and existing relationship studies. The implications of perceived similarity, rather than actual similarity, being predictive of attraction in existing relationships are discussed.

Improvements in the CHARMM all-atom force field for atomic-level molecular simulations of lipids are reported. Substantial adjustments have been made to the Lennard-Jones (LJ) hydrocarbon and torsional parameters and to the partial atomic charges and torsional parameters of the phosphate moiety. These changes were motivated by a combination of unexpected simulation results and recent high-level ab initio quantum mechanical calculations. The parameter optimization procedure is described, and the resulting energy function validated by an 11 ns molecular dynamics simulation of a hydrated phospholipid bilayer. Of note is the influence of the hydrocarbon LJ parameters on the conformational properties of the aliphatic tails, emphasizing the importance of obtaining the proper balance between the bonded and nonbonded portions of the force field. Compatibility with the CHARMM all-atom parameter sets for proteins and nucleic acids has been maintained such that high quality simulations of biologically interesting membranes are possible. The complete force field is included as Supporting Information and is available from www.pharmacy.umaryland.edu/∼alex.

Polyunsaturated lipids are an essential component of biological membranes, influencing order and dynamics of lipids, protein-lipid interaction, and membrane transport properties. To gain an atomic level picture of the impact of polyunsaturation on membrane properties, quantum mechanical (QM) and empirical force field based calculations have been undertaken. The QM calculations of the torsional energy surface for rotation about vinyl-methylene bonds reveal low barriers to rotation, indicating an intrinsic propensity toward flexibility. Based on QM and experimental data, empirical force field parameters were developed for polyunsaturated lipids and applied in a 16 ns molecular dynamics (MD) simulation of a 1-stearoyl-2-docosahexaenoyl-sn-glyerco-3-phosphocholine (SDPC) lipid bilayer. The simulation results are in good agreement with experimental data, suggesting an unusually high degree of conformational flexibility of polyunsaturated hydrocarbon chains in membranes. The detailed analysis of chain conformation and dynamics by simulations is aiding the interpretation of experimental data and is useful for understanding the unique role of polyunsaturated lipids in biological membranes. The complete force field is included as Supporting Information and is available from http://www.pharmacy.umaryland.edu/faculty/amackere/research.html.

A micromechanical torsion oscillator has been used to strengthen the limits on new Yukawa forces by determining the Casimir pressure between two gold-coated plates. By significantly reducing the random errors and obtaining the electronic parameters of the gold coatings, we were able to conclusively exclude the predictions of large thermal effects below $1\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ and strengthen the constraints on Yukawa corrections to Newtonian gravity in the interaction range from 29.5 nm to 86 nm.

The first precise measurement of the Casimir force between dissimilar metals is reported. The attractive force, between a Cu layer evaporated on a microelectromechanical torsional oscillator and an Au layer deposited on an ${\mathrm{A}\mathrm{l}}_{2}{\mathrm{O}}_{3}$ sphere, was measured dynamically with a noise level of $6\text{ }\text{ }\mathrm{f}\mathrm{N}/\sqrt{\mathrm{H}\mathrm{z}}$. Measurements were performed for separations in the $0.2--2\text{ }\ensuremath{\mu}\mathrm{m}$ range. The results agree to better than $1%$ in the $0.2--0.5\text{ }\ensuremath{\mu}\mathrm{m}$ range with a theoretical model that takes into account the finite conductivity and roughness of the two metals. The observed discrepancies, which are much larger than the experimental precision, can be attributed to a lack of a complete characterization of the optical properties of the specific samples used in the experiment.

To evaluate the veracity of models of the mere exposure effect and to understand the processes that moderate the effect, we conducted a meta-analysis of the influence of repeated exposure on liking, familiarity, recognition, among other evaluations. We estimated parameters from 268 curve estimates drawn from 81 articles and revealed that the mere exposure effect was characterized by a positive slope and negative quadratic effect consistent with an inverted-U shaped curve. In fact, such curves were associated with (a) all visual, but not auditory stimuli; (b) exposure durations shorter than 10 s and longer than 1 min; (c) both homogeneous and heterogeneous presentation types; and (d) ratings that were taken after all stimuli were presented. We conclude that existing models for the mere exposure effect do not adequately account for the findings, and we provide a framework to help guide future research. (PsycINFO Database Record

This research investigated two competing explanations of the similarity effect: Byrne’s (1971) reinforcement model and the information processing perspective. A meta-analysis of 240 laboratory-based similarity studies explored moderators important to the similarity effect, including set size, proportion of similarity, centrality of attitudes, and information salience. Results indicated effects for proportion of similarity, centrality of attitudes, and information salience, and were largely consistent with predictions of the information processing perspective. We discuss the implications of these findings for the two perspectives, for other models for the similarity effect, and for the role of affect and cognition in the experience of interpersonal attraction.

Eight molecular dynamics simulations of a hydrated lipid bilayer have been carried out differing only in the applied surface tension, γ, defining the boundary conditions of the periodic cell. The calculated surface area per molecule and deuterium order parameter profile are found to depend strongly on γ. We present several methods to calculate the area compressibility modulus, KA, from the simulations. Equivalence between the constant area and constant surface tension ensembles is investigated by comparing the present simulations with earlier work from our laboratories and we find simulation results to depend much more strongly on the specified surface area or surface tension than on the ensemble employed.

Rhodopsin, the G protein-coupled receptor primarily responsible for sensing light, is found in an environment rich in polyunsaturated lipid chains and cholesterol. Biophysical experiments have shown that lipid unsaturation and cholesterol both have significant effects on rhodopsin's stability and function; omega-3 polyunsaturated chains, such as docosahexaenoic acid (DHA), destabilize rhodopsin and enhance the kinetics of the photocycle, whereas cholesterol has the opposite effect. Here, we use molecular dynamics simulations to investigate the possibility that polyunsaturated chains modulate rhodopsin stability and kinetics via specific direct interactions. By analyzing the results of 26 independent 100-ns simulations of dark-adapted rhodopsin, we found that DHA routinely forms tight associations with the protein in a small number of specific locations qualitatively different from the nonspecific interactions made by saturated chains and cholesterol. Furthermore, the presence of tightly packed DHA molecules tends to weaken the interhelical packing. These results are consistent with recent NMR work, which proposes that rhodopsin binds DHA, and they suggest a molecular rationale for DHA's effects on rhodopsin stability and kinetics.

We derive an expression relating the static dielectric permittivity profile for a system nonuniform in one dimension to correlations between the net system dipole moment and the local polarization density. The permittivity profile of a dipalmitoylphosphatidylcholine (DPPC) lipid bilayer in water is calculated from an all-atom 20-ns molecular dynamics simulation. The component of the permittivity parallel to the bilayer shows a nonmonotonic decrease from the value in bulk water to the value in the membrane interior; the interfacial region itself has a very large permittivity, greater than that of bulk water. In high-dielectric regions, obtaining a quantitative estimate of the component normal to the bilayer is not possible because of large numerical uncertainty. However, the calculated correlation function is consistent with a value for the interface at least as large as that of bulk water. In general, the transition to a low-dielectric environment is sharp and is located on the inner border of the region where there is significant probability of finding the polar head groups.

We report new constraints on extra-dimensional models and other physics beyond the standard model based on measurements of the Casimir force between two dissimilar metals for separations in the range $0.2--1.2\ensuremath{\mu}\mathrm{m}.$ The Casimir force between a Au-coated sphere and a Cu-coated plate of a microelectromechanical torsional oscillator was measured statically with an absolute error of 0.3 pN. In addition, the Casimir pressure between two parallel plates was determined dynamically with an absolute error of $\ensuremath{\approx}0.6\mathrm{mPa}.$ Within the limits of experimental and theoretical errors, the results are in agreement with a theory that takes into account the finite conductivity and roughness of the two metals. The level of agreement between experiment and theory was then used to set limits on the predictions of extra-dimensional physics and thermal quantum field theory. It is shown that two theoretical approaches to the thermal Casimir force which predict effects linear in temperature are ruled out by these experiments. Finally, constraints on Yukawa corrections to Newton's law of gravity are strengthened by more than an order of magnitude in the range 56--330 nm.

Over the last three decades, colleges and universities increasingly have been expected to be accountable for the quality of undergraduate education. Although focused on K-12 education, A Nation at ...

We report the first isoelectronic differential force measurements between an Au-coated probe and two Au-coated films, made out of Au and Ge. These measurements, performed at submicron separations using soft microelectromechanical torsional oscillators, eliminate the need for a detailed understanding of the probe-film Casimir interaction. The observed differential signal is directly converted into limits on the parameters $\ensuremath{\alpha}$ and $\ensuremath{\lambda}$ which characterize Yukawa-like deviations from Newtonian gravity. We find $\ensuremath{\alpha}\ensuremath{\lesssim}{10}^{12}$ for $\ensuremath{\lambda}\ensuremath{\sim}200\text{ }\text{ }\mathrm{nm}$, an improvement of $\ensuremath{\sim}10$ over previous limits.

Insufficient supply to the developing brain of docosahexaenoic acid (22:6n3, DHA), or its ω-3 fatty acid precursors, results in replacement of DHA with docosapentaenoic acid (22:5n6, DPA), an ω-6 fatty acid that is lacking a double bond near the chain's methyl end. We investigated membranes of 1-stearoyl(d35)-2-docosahexaenoyl-sn-glycero-3-phosphocholine and 1-stearoyl(d35)-2-docosapentaenoyl-sn-glycero-3-phosphocholine by solid-state NMR, X-ray diffraction, and molecular dynamics simulations to determine if the loss of this double bond alters membrane physical properties. The low order parameters of polyunsaturated chains and the NMR relaxation data indicate that both DHA and DPA undergo rapid conformational transitions with correlation times of the order of nanoseconds at carbon atom C2 and of picoseconds near the terminal methyl group. However, there are important differences between DHA- and DPA-containing lipids: the DHA chain with one additional double bond is more flexible at the methyl end and isomerizes with shorter correlation times. Furthermore, the stearic acid paired with the DHA in mixed-chain lipids has lower order, in particular in the middle of the chain near carbons C10-12, indicating differences in the packing of hydrocarbon chains. Such differences are also reflected in the electron density profiles of the bilayers and in the simulation results. The DHA chain has a higher density near the lipid−water interface, whereas the density of the stearic acid chain is higher in the bilayer center. The loss of a single double bond from DHA to DPA results in a more even distribution of chain densities along the bilayer normal. We propose that the function of integral membrane proteins such as rhodopsin is sensitive to such a redistribution.

Recent isothiocyanate covalent labeling studies have suggested that a classical cannabinoid, (−)-7′-isothiocyanato-11-hydroxy-1′,1′dimethylheptyl-hexahydrocannabinol (AM841), enters the cannabinoid CB2 receptor via the lipid bilayer (Pei, Y., Mercier, R. W., Anday, J. K., Thakur, G. A., Zvonok, A. M., Hurst, D., Reggio, P. H., Janero, D. R., and Makriyannis, A. (2008) Chem. Biol. 15, 1207–1219). However, the sequence of steps involved in such a lipid pathway entry has not yet been elucidated. Here, we test the hypothesis that the endogenous cannabinoid sn-2-arachidonoylglycerol (2-AG) attains access to the CB2 receptor via the lipid bilayer. To this end, we have employed microsecond time scale all-atom molecular dynamics (MD) simulations of the interaction of 2-AG with CB2 via a palmitoyl-oleoyl-phosphatidylcholine lipid bilayer. Results suggest the following: 1) 2-AG first partitions out of bulk lipid at the transmembrane α-helix (TMH) 6/7 interface; 2) 2-AG then enters the CB2 receptor binding pocket by passing between TMH6 and TMH7; 3) the entrance of the 2-AG headgroup into the CB2 binding pocket is sufficient to trigger breaking of the intracellular TMH3/6 ionic lock and the movement of the TMH6 intracellular end away from TMH3; and 4) subsequent to protonation at D3.49/D6.30, further 2-AG entry into the ligand binding pocket results in both a W6.48 toggle switch change and a large influx of water. To our knowledge, this is the first demonstration via unbiased molecular dynamics that a ligand can access the binding pocket of a class A G protein-coupled receptor via the lipid bilayer and the first demonstration via molecular dynamics of G protein-coupled receptor activation triggered by a ligand binding event.

This highly accessible and innovative text with supporting web site uses Excel (R) to teach the core concepts of econometrics without advanced mathematics. It enables students to use Monte Carlo simulations in order to understand the data generating process and sampling distribution. Intelligent repetition of concrete examples effectively conveys the properties of the ordinary least squares (OLS) estimator and the nature of heteroskedasticity and autocorrelation. Coverage includes omitted variables, binary response models, basic time series, and simultaneous equations. The authors teach students how to construct their own real-world data sets drawn from the internet, which they can analyze with Excel (R) or with other econometric software. The accompanying web site with text support can be found at www.wabash.edu/econometrics.

The British choice in Iraq has been characterized as “Tony Blair's War,” with many believing that the personality and leadership style of the prime minister played a crucial part in determining British participation. Is this the case? To investigate, I employ at-a-distance measures to recover Blair's personality from his responses to foreign policy questions in the House of Commons. I find that he has a high belief in his ability to control events, a low conceptual complexity, and a high need for power. Using newly available evidence on British decision making, I show how Blair's personality and leadership style did indeed shape both the process and outcome of British foreign policy toward Iraq. The research reemphasizes the importance of individual level factors in theories of foreign policy, as well as offering a comprehensive explanation of a critical episode.

Previous theorizing by clinical psychologists suggests that adolescent narcissism may be related to parenting practices (Kernberg, 1975; Kohut, 1977). Two studies investigated the relations between parenting dimensions (i.e., warmth, monitoring, and psychological control) and narcissism both with and without removing from narcissism variance associated with trait self-esteem. Two hundred and twenty-two college students (Study 1) and 212 high school students (Study 2) completed the Narcissistic Personality Inventory, a trait self-esteem scale, and standard measures of the three parenting dimensions. Parental warmth was associated positively and monitoring was associated negatively with both types of narcissism. Psychological control was positively associated with narcissism scores from which trait self-esteem variance had been removed. Clinical implications of the findings are discussed, limitations are addressed, and future research directions are suggested.

The seventeenth-century conflict between patriarchal and liberal political thought grew out of a shift in views on the nature of man and society. Sir Robert Filmer insisted that the king ruled absolutely, the divinely ordained father of his people. Sidney, Tyrrell, and Locke grounded political power in an act of consent on the part of free-born individuals. To what extent did these changing beliefs about human nature also bring about new perspectives on the nature, role and status of women? While this aspect of political theory has usually remained unexplored, it was an important critical weapon in the battle between patriarchal and liberal thought. Patriarchal theorists, relying on the Book of Genesis, could assign women to an appropriately subordinate place in family and society. Consent theories, though, as Filmer noted, depended for consistency on the inclusion of women (as well as children) in the formation of civil society. Early liberal writers including Tyrrell and Sidney were unwilling, then, to abandon patriarchal theory in all its forms and insisted that the consent of the “promiscuous multitude” of women and children was unnecessary. John Locke never specifically dealt with the role of women in the formation of society. Thus, he seemed to have escaped some of the difficulties of finding a place for women consistent with both traditional views of female status and newer views of human nature. Where Locke did speak directly about women, he often departed from traditional views in favor of an individualist approach. Examples of this may be found in his comments on marriage, education and in his discussion of female preaching.

The decay energy spectrum for neutron unbound states in 24O (Z=8, N=16) has been observed for the first time. The resonance energy of the lowest lying state, interpreted as the 2+ level, has been observed at a decay energy above 600 keV. The resulting excitation energy of the 2+ level above 4.7 MeV, supplies strong evidence that 24O is a doubly magic nucleus. The data is also consistent with the presence of a second excited state around 5.33 MeV which can be interpreted as the 1+ level.