Towards Initial Mass Functions for Asteroids and Kuiper Belt Objects

Our goal is to understand primary accretion of the first planetesimals. The primitive meteorite record suggests that sizeable planetesimals formed in the asteroid belt over a period longer than a million years, each composed entirely of an unusual, but homogeneous, mixture of mm-size particles. We sketch a scenario in which primary accretion of 10-100km size planetesimals proceeds directly, if sporadically, from aerodynamically-sorted mm-size particles (generically "chondrules"). These planetesimal sizes are in general agreement with the currently observed asteroid mass peak near 100km diameter, which has been identified as a "fossil" property of the pre-erosion, pre-depletion population. We extend our primary accretion theory to make predictions for outer solar system planetesimals, which may also have a preferred size in the 100km diameter range. We estimate formation rates of planetesimals and assess the conditions needed to match estimates of both asteroid and Kuiper Belt Object (KBO) formation rates. For nebula parameters that satisfy observed mass accretion rates of Myr-old protoplanetary nebulae, the scenario is roughly consistent with not only the "fossil" sizes of the asteroids, and their estimated production rates, but also with the observed spread in formation ages of chondrules in a given chondrite, and with a tolerably small radial diffusive mixing during this time between formation and accretion (the model naturally helps explain the peculiar size distribution of chondrules within such objects). The scenario also produces 10-100km diameter primary KBOs. The optimum range of parameters, however, represents a higher gas density and fractional abundance of solids, and a smaller difference between keplerian and pressure-supported orbital velocities, than "canonical" models of the solar nebula. We discuss several potential explanations for these differences.Comment: Icarus, in pres

Time-delayed models of gene regulatory networks

We discuss different mathematical models of gene regulatory networks as relevant to the onset and development of cancer. After discussion of alternativemodelling approaches, we use a paradigmatic two-gene network to focus on the role played by time delays in the dynamics of gene regulatory networks. We contrast the dynamics of the reduced model arising in the limit of fast mRNA dynamics with that of the full model. The review concludes with the discussion of some open problems

Master of Science

thesisAlthough couples research tends to focus on interactions of high salience interactions, it is likely that couples spend the majority of their time engaged in interactions of low salience (i.e., completing chores, having everyday conversations, being in the same physical space). Theory suggests that physiological functioning should be more efficient when in the presence of a spouse during both low- and high-salience interactions. It is likely that this increased efficiency in physiological functioning may be observed in a decrease in high-frequency heart rate variability (HF-HRV). The purpose of this study was to determine how much time couples spend engaged in both low- and high-salience interactions, whether physiological functioning is more efficient in the presence of a spouse during a low-salience interaction than alone, and whether relationship satisfaction moderates this change in functioning. Participants completed two consecutive 5-minute resting baselines, one in the presence of their spouse and one alone. Consistent with predictions, participants reported spending significantly more time engaged in low-salience interactions than high-salience interactions. Further, results indicated a significant increase in HF-HRV for participants who completed their first baseline alone and had their spouse reintroduced for the second baseline. No significant effects were found for heart rate or moderation by relationship satisfaction. Taken together, results suggest that participants are experiencing physiological stress during baseline. Additionally, anticipation of conflict in the study may turn one's spouse into a stressor during baseline. Limitations and future directions are discussed

International Conflict and Collective Security: The Principle of Concern in International Organization

The control of man’s violence against man presents to modern society its greatest problem. A capacity to deal with the most devastating type of conflict—international war—is crucial to human welfare and even to the survival of civilization. Nations have become interdependent in technology and economy, but world political organization is based on a system of sovereign states now divided into hostile camps armed with absolute weapons. This book is a study of the development of collective security, or international cooperative action for the maintenance of peace. The approach is based upon the “principle of concern,” a recognition of the fact that organization to preserve peace is essential for every political community. As a case study Willard N. Hogan has analyzed the principle of collective security as it has worked in practice in international organizations over the past thirty-five years. He holds that collective security is not unworkable as a method for stopping aggression and maintaining peace. Willard Hogan is professor of political science at State University Teachers College, New Paltz, New York, and director of the Information Center for the United Nations at the same college.https://uknowledge.uky.edu/upk_political_science_international_relations/1009/thumbnail.jp

Scales of the Extra Dimensions and their Gravitational Wave Backgrounds

Circumstances are described in which symmetry breaking during the formation of our three-dimensional brane within a higher-dimensional space in the early universe excites mesoscopic classical radion or brane-displacement degrees of freedom and produces a detectable stochastic background of gravitational radiation. The spectrum of the background is related to the unification energy scale and the the sizes and numbers of large extra dimensions. It is shown that properties of the background observable by gravitational-wave observatories at frequencies $f\approx 10^{-4}$ Hz to $10^3$ Hz contain information about unification on energy scales from 1 to $10^{10}$ TeV, gravity propagating through extra-dimension sizes from 1 mm to $10^{-18}$mm, and the dynamical history and stabilization of from one to seven extra dimensions.Comment: 6 pages, Latex, 1 figure, submitted to Phys. Re

Collision of High Frequency Plane Gravitational and Electromagnetic Waves

We study the head-on collision of linearly polarized, high frequency plane gravitational waves and their electromagnetic counterparts in the Einstein-Maxwell theory. The post-collision space-times are obtained by solving the vacuum Einstein-Maxwell field equations in the geometrical optics approximation. The head-on collisions of all possible pairs of these systems of waves is described and the results are then generalised to non-linearly polarized waves which exhibit the maximum two degrees of freedom of polarization.Comment: Latex file, 17 pages, accepted for publication in International Journal of Modern Physics

The Statistics of Subtypes: A Proposed Study Investigating Statistical Learning Across Subtypes of Dyslexia

Current research regarding dyslexia and its subtypes is inconsistent. There are discrepancies in the literature surrounding the causes and manifestations of dyslexia. Furthermore, there is very little research concerning the role of statistical learning in differentiating between subtypes of dyslexia. The purpose of the proposed study is to quantify the differences in statistical learning ability across three subtypes of dyslexia (i.e., phonological dyslexia, surface dyslexia, and deep dyslexia). It is predicted that participants with a dyslexia diagnosis of any subtype will be worse at using statistics to find word boundaries than control participants. Additionally, it is hypothesized that participants with surface dyslexia will express the highest capacity for statistical learning among the three subtypes. Finally, it is hypothesized that participants belonging to the deep dyslexia subgroup will express the lowest capacity for statistical learning. Participants from each of the four treatments (i.e., phonological dyslexia, surface dyslexia, deep dyslexia, and control) will be exposed to the same auditory nonsense word stream. After finishing the listening phase, all participants will complete a forced-choice recognition task. The task will be to indicate which of the two sound strings sounds most like a word from the nonsense language. If the results of this study show that there are differences in statistical learning ability between different subtypes of dyslexia, treatments and interventions can be tailored more appropriately to individuals belonging to each subtype. Additionally, it will be possible to highlight early risk factors that can help with early identification of dyslexia in children