125 research outputs found
Bifurcations of equilibria in DNA elasticity
No full textDNA molecules in the familiar double helical B form are treated here as though they have rod-like structures obtained by stacking the
nearly planar base pairs comprising them one on top of another with each rotated by approximately one-tenth of a full turn with respect
to its immediate predecessor in the stack. As each base in a base pair is attached to the sugar-phosphate backbone chain of one of the
two DNA strands that have come together to form the Watson-Crick structure, and each phosphate group in a backbone chain bears one electronic charge, two such charges are associated with each base pair. Thus, each base pair is subject to not only the elastic forces and moments exerted on it by its neighboring base pairs but also to remote electrostatic forces that, because they are only partially screened out by positively charged counter ions, can render the molecule's equilibrium configurations sensitive to changes in the concentration c of salt in the medium.
The observation that the step from one base pair to the next can be one of several distinct types, each having its own mechanical properties that depend on the nucleotide composition of the step, and the assumption that a base pair is rigid, led to the development of a theory of sequence dependent DNA elasticity [Coleman, Olson, and Swigon, J. Chem. Phys. 118 ,7127-7140, (2003)]. The theory of DNA molecules in aqueous solution developed here is based on but goes beyond that theory. It takes into account the intramolecular electrostatic interactions of the negatively charged phosphate groups in the molecule and the impenetrability of the DNA molecule for cases in which the
electrostatic repulsive forces do not suffice to avoid self penetration. The theory permits one to calculate equilibrium configurations, to determine their stability, and to study the dependence of them on salt concentration and on all kinds of end conditions.
When the intramolecular electrostatic forces are taken into account, the equations of mechanical equilibrium for a DNA molecule with N+1 base pairs are a system of mu*N non-linear equations, where mu, the number of kinematical variables describing the relative displacement and orientation of adjacent base pairs is in general 6; it reduces to 3 when base-pair steps are assumed to be inextensible and non-shearable. An efficient numerically stable computational scheme is here presented for
solving those equations and determining the mechanical stability of the calculated equilibrium configurations. That scheme is employed to compute and analyze bifurcation diagrams in which c is the bifurcation parameter and to show that, for an intrinsically curved molecule, small changes in c can have a strong effect on stable
equilibrium configurations. Cases are presented in which self-contact must be taken into account even though the intramolecular electrostatic forces of repulsion are strong.Ph.D.Includes bibliographical references (p. 106-110)
Pre- versus Post-Menopausal Onset of Overactive Bladder and the Response to Vaginal Estrogen Therapy: A Prospective Study
No full textBackground and Objectives: This study examined the utility of local estrogen therapy for improving urinary symptoms in women diagnosed with Overactive Bladder allied to the time of onset of urinary symptoms whether pre- or post-menopausal. Materials and Methods: Subject to informed consent, menopausal women diagnosed with Overactive Bladder (OAB) and Genitourinary Syndrome of Menopause (GSM) were enrolled at three urogynecological units. OAB symptoms were scored using the Global Pelvic Floor Symptoms Bother Questionnaire (GPFSBQ), with explicit attention to question number 3 that specifically addresses the presence or absence of urgency and the Patient Perception of Intensity of Urgency Scale (PPIUS). The Vaginal Health Index (VHI) was used to assess the vaginal mucosa trophism. Exclusion criteria included: Pelvic organ prolapse (POP) ≥ stage II, urinary tract infection or disease, diabetes, inflammatory diseases, use of diuretics, alcohol or drug addictions, neurological and/or psychiatric disorders, and other precluding conditions. Women were treated with local estrogens for 3 months and re-evaluated. Results: Forty-three post-menopausal women were enrolled. Of these, ten women developed OAB symptoms before menopause (Group I) and 33 developed symptoms after menopause (Group II). Following local estrogen therapy, based on the Global Pelvic Floor Symptoms Bother Questionnaire, improvement of OAB symptoms was reported by 20% of patients in Group I (p = 0.414) and 64% of patients in Group II, (p = 0.002). Based on the PPIUS scale, diminution in urinary urgency was experienced by 20% of patients in Group I (p = 0.68) and 66% of patients in Group II (p = 0.036). Improved VHI scores were graded statisticaly significant in both groups (Group I in 100% of women, p = 0.005 vs. 76% in Group II, p = 0.004). Conclusions: Our results indicate that local estrogen therapy is more effective in women who develop OAB after menopause
How do monkeys view faces?—a study of eye movements
No full textFace perception plays a crucial role in primate social communication. We have investigated the pattern of eye movements produced by rhesus monkeys (Macaca mulatta) as they viewed images of faces. Eye positions were recorded accurately using implanted eye coils, while neutral upright, inverted and scrambled images of monkey and human faces were presented on a computer screen. The monkeys exhibited a similar eye scan pattern while viewing familiar and unfamiliar monkey face images, or while viewing monkey and human face images. No differences were observed in the distribution of viewing times, number of fixations, time into the trial of first saccade to local facial features, and the temporal and spatial characteristics of viewing patterns across the facial images. However, there was a greater probability of re-fixation of the eye region of unfamiliar faces during the first few seconds of the trial suggesting that the eyes are important for the initial encoding of identity. Indeed, the highest fixation density was found in the eye region of all the face images. The viewing duration and the number of fixations per image decreased when inverted or scrambled faces were presented. The eye region in these modified images remained the primary area of fixation. However, the number of fixations directed to the eyes decreased monotonically from the upright images through the inverted versions to the scrambled face images. Nonetheless, the eyes remain the most salient facial substructure regardless of the arrangement of other features, although the extent of salience which they attain may depend both on the low level properties of the eyes and on the global arrangement of facial features
A policy model for Tunisia with real and financial flows
No full textThis model was developed to provide a moacroeconomic framework for Tunisia's structural adjustment program and a flexible tool for further country economic analysis. As currently specified, it is designed to analyze fiscal, debt, and incomes policies, while deriving implications for the exchange rate and for the availability of credit to the private sector. Several policy experiments are carried out to illustrate this focus, and suggestions are offered for variations in model closure and detail.Economic Theory&Research,Environmental Economics&Policies,Banks&Banking Reform,Economic Stabilization,Financial Intermediation
Credit rationing, tenancy, productivity, and the dynamics of inequality
No full textWhy, when given the same resources, might productivity be lower on farms operated through sharecropping than on owner-run farms? The reason is that sharecropping, much less wage contracts, cannot overcome the divergence of interests between those who till the land and those who own it. Only land redistribution can do that. This paper presents notes toward a general equilibrium theory of land tenancy that suggest how changes in technology and publicly provided infrastructure can affect the equilibrium distribution of land in countries where credit is rationed. When credit to famers is rationed, changes in technology can increase the inequality in landholdings - with a long term increase in share tenancy. This is turn might reduce productivity, at least partially offsetting the initial improvements. The paper suggests that the development of effective rural financial institutions would reduce the likelihood of these negative effects on equality and productivity. It further cautions though that past attempts in creating such institutions have failed because of a lack of accountability and of enforcement procedures.Environmental Economics&Policies,Economic Theory&Research,Banks&Banking Reform,Economic Growth,Municipal Financial Management
Recommended from our members
Arab Jews, Mizrahi studies and Shimon Ballas' Outcast
No full texttextThis report examines the novel Outcast by Israeli author Shimon Ballas and its themes in respect to the prominent debates in the field of Mizrahi studies. It discusses the prominent scholars who deal with the history of Arab Jews in Israel and Mizrahi studies in general. It examines these issues both in the scholarship and literature and posits that each adds to and complicates the debate. The discussion also includes the treatments of Arab Jews in modern Zionist discourse and the history of Mizrahi political and scholarly activity in Israel.Middle Eastern Studie
Review of the Change 2010-2017
No full textReview of changes made by journals to their author instructions in light of the replication crisis, between 2010 and 201
Review of the Change 2010-2017
No full textReview of changes made by journals to their author instructions in light of the replication crisis, between 2010 and 201
Sarcasm Detection is Way Too Easy! An Empirical Comparison of Human and Machine Sarcasm Detection
No full textRecently, author-annotated sarcasm datasets, which focus on intended, rather than perceived sarcasm, have been introduced. Although datasets collected using first-party annotation have important benefits, there is no comparison of human and machine performance on these new datasets. In this paper, we collect new annotations to provide human-level benchmarks for these first-party annotated sarcasm tasks in both English and Arabic, and compare the performance of human annotators to that of state-of-the-art sarcasm detection systems. Our analysis confirms that sarcasm detection is extremely challenging, with individual humans performing close to or slightly worse than the best trained models. With majority voting, however, humans are able to achieve the best results on all tasks. We also perform error analysis, finding that some of the most challenging examples are those that require additional context. We also highlight common features and patterns used to express sarcasm in English and Arabic such as idioms and proverbs. We suggest that to better capture sarcasm, future sarcasm detection datasets and models should focus on representing conversational and cultural context while leveraging world knowledge and common sense
- …
