Model for the unidirectional motion of a dynein molecule

Cytoplasmic dyneins transport cellular organelles by moving on a microtubule filament. It has been found recently that depending on the applied force and the concentration of the adenosine triphosphate (ATP) molecules, dynein's step size varies. Based on these studies, we propose a simple model for dynein's unidirectional motion taking into account the variations in its step size. We study how the average velocity and the relative dispersion in the displacement vary with the applied load. The model is amenable to further extensions by inclusion of details associated with the structure and the processivity of the molecule.Comment: 10 pages, 5 figure

Dynamic instability of microtubules: effect of catastrophe-suppressing drugs

Microtubules are stiff filamentary proteins that constitute an important component of the cytoskeleton of cells. These are known to exhibit a dynamic instability. A steadily growing microtubule can suddenly start depolymerizing very rapidly; this phenomenon is known as ``catastrophe''. However, often a shrinking microtubule is ``rescued'' and starts polymerizing again. Here we develope a model for the polymerization-depolymerization dynamics of microtubules in the presence of {\it catastrophe-suppressing drugs}. Solving the dynamical equations in the steady-state, we derive exact analytical expressions for the length distributions of the microtubules tipped with drug-bound tubulin subunits as well as those of the microtubules, in the growing and shrinking phases, tipped with drug-free pure tubulin subunits. We also examine the stability of the steady-state solutions.Comment: Minor corrections; final published versio

The Use of Socratic Seminar in Teaching Speaking on Hortatory Exposition Text

This research was conducted to the eleventh grade students of SMA Negeri 2 Pontianak in academic year 2013/2014. The purposes are to know whether or not the use of Socratic Seminar technique effective in teaching speaking on hortatory exposition text and to know how significant the effectiveness of the use of Socratic Seminar is in improving students\u27 speaking on hortatory exposition text. A Quasi-experimental with non-equivalent control group design was used by the writer as the research method. Cluster sampling is the technique sampling and the samples of this research were class IPA 3 as the experimental group and class IPA 4 as the control group. The computation of t-test is higher than t-table, thereforethe alternative hypothesis is accepted. The effect size of the treatment was 0.99 and it was qualified as very strong. The results of this research arethe Socratic Seminar technique is effective andstrong effect toward students\u27 speaking achievement

Association of Expired Nitric Oxide with Occupational Particulate Exposure

Particulate air pollution has been associated with adverse respiratory health effects. This study assessed the utility of expired nitric oxide to detect acute airway responses to metal-containing fine particulates. Using a repeated-measures study design, we investigated the association between the fractional concentration of expired nitric oxide (F$_E$NO) and exposure to particulate matter with an aerodynamic mass median diameter of less than or equal to 2.5 micro m (PM$_{2.5}$) in boilermakers exposed to residual oil fly ash and metal fumes. Subjects were monitored for 5 days during boiler repair overhauls in 1999 (n = 20) or 2000 (n = 14). The Wilcoxon median baseline F$_E$NO was 10.6 ppb [95% confidence interval (CI): 9.1, 12.7] in 1999 and 7.4 ppb (95% CI: 6.7, 8.0) in 2000. The Wilcoxon median PM$_{2.5}$ 8-hr time-weighted average was 0.56 mg/m(3) (95% CI: 0.37, 0.93) in 1999 and 0.86 mg/m(3) (95% CI: 0.65, 1.07) in 2000. F$_E$NO levels during the work week were significantly lower than baseline F$_E$NO in 1999 (p < 0.001). A significant inverse exposure-response relationship between log-transformed F$_E$NO and the previous workday's PM$_{2.5}$ concentration was found in 1999, after adjusting for smoking status, age, and sampling year. With each 1 mg/m$^3$ incremental increase in PM$_{2.5}$ exposure, log F$_E$NO decreased by 0.24 (95% CI: -0.38, -0.10) in 1999. The lack of an exposure-response relationship between PM$_{2.5}$ exposure and F$_E$NO in 2000 could be attributable to exposure misclassification resulting from the use of respirators. In conclusion, occupational exposure to metal-containing fine particulates was associated with significant decreases in F$_E$NO in a survey of workers with limited respirator usage

Birth prevalence of neural tube defects and orofacial clefts in India: a systematic review and meta-analysis.

BACKGROUND: In the last two decades, India has witnessed a substantial decrease in infant mortality attributed to infectious disease and malnutrition. However, the mortality attributed to birth defects remains constant. Studies on the prevalence of birth defects such as neural tube defects and orofacial clefts in India have reported inconsistent results. Therefore, we conducted a systematic review of observational studies to document the birth prevalence of neural tube defects and orofacial clefts. METHODS: A comprehensive literature search for observational studies was conducted in MEDLINE and EMBASE databases using key MeSH terms (neural tube defects OR cleft lip OR cleft palate AND Prevalence AND India). Two reviewers independently reviewed the retrieved studies, and studies satisfying the eligibility were included. The quality of included studies was assessed using selected criteria from STROBE statement. RESULTS: The overall pooled birth prevalence (random effect) of neural tube defects in India is 4.5 per 1000 total births (95% CI 4.2 to 4.9). The overall pooled birth prevalence (random effect) of orofacial clefts is 1.3 per 1000 total births (95% CI 1.1 to 1.5). Subgroup analyses were performed by region, time period, consanguinity, and gender of newborn. CONCLUSION: The overall prevalence of neural tube defects from India is high compared to other regions of the world, while that of orofacial clefts is similar to other countries. The majority of studies included in the review were hospital based. The quality of these studies ranged from low to moderate. Further well-designed, high quality community-based observational studies are needed to accurately estimate the burden of neural tube defects and orofacial clefts in India

Scaling of fluctuation for Directed polymers with random interaction

Using a finite size scaling form for reunion probability, we show numerically the existence of a binding-unbinding transition for Directed polymers with random interaction. The cases studied are (A1) two chains in 1+1 dimensions, (A2) two chains in 2+1 dimensions and (B) three chains in 1+1 dimensions. A similar finite size scaling form for fluctuation establishes a disorder induced transition with identical exponents for cases A2 and B. The length scale exponents in all the three cases are in agreement with previous exact renormalization group results.Comment: Revtex, 4 postscript figures available on request (email: [email protected]); To appear in J. Phys. A Letter

Pensions and the health of older people in South Africa: Is there an effect?

This paper critically reviews evidence from low and middle income countries that pensions are associated with better health outcomes for older people. It draws on new, nationally representative survey data from South Africa to provide a systematic analysis of pension effects on health and quality of life. It reports significant associations with the frequency of health service utilisation, as well as with awareness and treatment of hypertension. There is, however, no association with actual control of hypertension, self-reported health or quality of life. The paper calls for a more balanced and integrated approach to social protection for older people

Reunion of random walkers with a long range interaction: applications to polymers and quantum mechanics

We use renormalization group to calculate the reunion and survival exponents of a set of random walkers interacting with a long range $1/r^2$ and a short range interaction. These exponents are used to study the binding-unbinding transition of polymers and the behavior of several quantum problems.Comment: Revtex 3.1, 9 pages (two-column format), 3 figures. Published version (PRE 63, 051103 (2001)). Reference corrections incorporated (PRE 64, 059902 (2001) (E

Steric repulsion and van der Waals attraction between flux lines in disordered high Tc superconductors

We show that in anisotropic or layered superconductors impurities induce a van der Waals attraction between flux lines. This attraction together with the disorder induced repulsion may change the low B - low T phase diagram significantly from that of the pure thermal case considered recently by Blatter and Geshkenbein [Phys. Rev. Lett. 77, 4958 (1996)].Comment: Latex, 4 pages, 1 figure (Phys. Rev. Lett. 79, 139 (1997)

Vicinal Surfaces, Fractional Statistics and Universality

We propose that the phases of all vicinal surfaces can be characterized by four fixed lines, in the renormalization group sense, in a three-dimensional space of coupling constants. The observed configurations of several Si surfaces are consistent with this picture. One of these fixed lines also describes one-dimensional quantum particles with fractional exclusion statistics. The featureless steps of a vicinal surface can therefore be thought of as a realization of fractional-statistics particles, possibly with additional short-range interactions.Comment: 6 pages, revtex, 3 eps figures. To appear in Physical Review Letters. Reference list properly arranged. Caption of Fig. 1 slightly reworded. Fig 3 (in color) is not part of the paper. It complements Fig.