Analysis of enhanced diffusion in Taylor dispersion via a model problem

We consider a simple model of the evolution of the concentration of a tracer, subject to a background shear flow by a fluid with viscosity $\nu \ll 1$ in an infinite channel. Taylor observed in the 1950's that, in such a setting, the tracer diffuses at a rate proportional to $1/\nu$, rather than the expected rate proportional to $\nu$. We provide a mathematical explanation for this enhanced diffusion using a combination of Fourier analysis and center manifold theory. More precisely, we show that, while the high modes of the concentration decay exponentially, the low modes decay algebraically, but at an enhanced rate. Moreover, the behavior of the low modes is governed by finite-dimensional dynamics on an appropriate center manifold, which corresponds exactly to diffusion by a fluid with viscosity proportional to $1/\nu$

Dispersion of biased swimming microorganisms in a fluid flowing through a tube

Classical Taylor-Aris dispersion theory is extended to describe the transport of suspensions of self-propelled dipolar cells in a tubular flow. General expressions for the mean drift and effective diffusivity are determined exactly in terms of axial moments, and compared with an approximation a la Taylor. As in the Taylor-Aris case, the skewness of a finite distribution of biased swimming cells vanishes at long times. The general expressions can be applied to particular models of swimming microorganisms, and thus be used to predict swimming drift and diffusion in tubular bioreactors, and to elucidate competing unbounded swimming drift and diffusion descriptions. Here, specific examples are presented for gyrotactic swimming algae.Comment: 20 pages, 4 figures. Published version available at http://rspa.royalsocietypublishing.org/content/early/2010/02/09/rspa.2009.0606.short?rss=

Peningkatan Aktivitas dan Hasil Belajar IPS melalui Pendekatan Keterampilan Proses

This research aims to improve the activity and results of student learning in Social Studies by using the process approach skills. The methods used in this research is the Classroom Action Research consisting of three cycles, each cycle includes planning, implementation, observation and reflection. The method of data collection using a written test and observation techniques. The result of this research shows that there is an increase in: (1) learning activities of students, the indicators are achieved at the second cycle as well as on the results of three cycles the better, (2) student learning outcomes, the second cycle the indicators also have reached the next three cycles of increasing and ≥ 75%.Penelitian ini bertujuan meningkatkan aktivitas dan hasil belajar siswa dalam pembelajaran Ilmu Pengetahuan Sosial (IPS) dengan menggunakan Pendekatan Keterampilan Proses. Metode yang digunakan dalam penelitian ini adalah Penelitian Tindakan Kelas (PTK) yang terdiri dari tiga siklus, setiap siklus meliputi perencanaan, pelaksanaan, observasi dan refleksi. Tehnik pengumpulan Data menggunakan tehnik observasi dan tes tertulis. Hasil penelitian ini menunjukkan adanya peningkatan pada: (1) aktivitas belajar siswa, indikator tercapai pada siklus kedua begitupun pada siklus tiga hasilnya semakin baik, (2) hasil belajar siswa, siklus kedua indikatornya juga sudah tercapai selanjutnya siklus tiga semakin meningkat dan ≥ 75%.   Â

An Assessment of Risk of Iodine Deficiency Among Pregnant Women in Sarawak, Malaysia

Previous findings from a state-wide Iodine Deficiency Disorders (IDD) study among pregnant women (PW) in Sarawak indicated that PW are at risk of IDD and further assessment is needed. This paper describes the methodology used in conducting this study for an assessment of risk of iodine deficiency among pregnant women in Sarawak, Malaysia. A total of 30 maternal child health care clinics (MCHCs) were selected using probability proportional to population size (PPS) sampling technique. The PW sample size was calculated based on 95% confidence interval (CI), relative precision of 5%, design effect of 2, anticipated IDD prevalence of 65.0% and non-response rate of 20%. Thus, the total sample size required was 750 (25 respondents per selected MCHC). The WHO Expanded Programme on Immunization (EPI) surveys approach was used to randomly select the first respondent and subsequent respondents were chosen until the required number of PW was met. The required data were obtained through: face-to-face interviews (socio-demographic and food frequency questionnaire), clinical assessments (thyroid size, and hyper/hypothyroidism) and biochemical analysis (urine and blood serum). A total of 677 PW responded in the study with a response rate of 90.2%. Majority of the PW were at second gravida, aged 25-29 years old and of Malay ethnicity. The methodology used in this study was based on International guidelines which may provide state's estimates. All the necessary steps were taken into consideration to ensure valid and reliable findings on current iodine status among PW

Deteksi Dan Identifikasi Cemaran Virus Avian Influenza Pada Pasar Tradisional Di Kabupaten Aceh Besar Dan Kota Banda Aceh

Penelitian ini dirancang untuk mendeteksi keberadaan virus AI pada beberapa titik kritis, yaitu unggas, kandang penampungan sementara, tempat pemotongan dan penjualan karkas, dan mengidentifikasi subtipe virus AI pada beberapa pasar tradisional di Kabupaten Aceh Besar dan Kota Banda Aceh, Propinsi Aceh. Sampel swab diambil secara acak (random) dari empat pasar di Kabupaten Aceh Besar dan Kota Banda Aceh, Propinsi Aceh, yaitu pasar Lambaro, Ketapang, Ulekareng dan Peunayong, dan dipoolkan. Satu pool sampel berisi 1 sampai 5 swab yang dikelompokkan berdasarkan pedagang, jenis unggas, dan titik kritis cemaran AI. Jumlahtotal sampel yang diambil adalah 314 swab, yang terdiri dari swab trakea unggas hidup, kandang penampungan, meja tempat pemotongan, dan karkas, kemudian dikelompokkan dalam 121 pool. Isolasi virus AI kedalam telur ayam bertunas (TAB), pemeriksaan secara serologis (uji HA/HI), dan identifikasi molekuler (metode RT-PCR) di lakukan di bagian Virologi Laboratorium Veteriner, dinas Kesehatan Hewan dan Peternakan Provinsi Aceh, dan Laboratorium Riset Terpadu Fakultas Kedokteran Hewan Universitas Syiah Kuala Banda Aceh. Analisis hasil pemeriksaan serologis dan identifikasi molekuler virus AI dilakukan dengan metode deskriptif. Hasilisolasi virus pada TAB menunjukkan bahwa embrio mengalami kematian pada 1 hari setelah di infeksikan dengan material virus dari sampel swab yang berasal dari pasar Lambaro Kabupaten Aceh Besar, dan titer antibodi terhadap virus AI hanya terdeteksi pada itik dan ayam pedaging yang berkisar antara 24 sampai dengan 27. Dari hasil serologis tersebut dilanjutkan dengan pemeriksaan RT-PCR. Berdasarkan hasil uji RT-PCR menggunakan primer spesifik terhadap gen M, H5, dan N1 diperoleh virus AI yang bersirkulasi pada unggas di pasar Lambaro tergolong subtipe H5N1. Hasil penelitian ini membuktikan bahwa diantara beberapa titik kritiscemaran virus AI di pasar tradisional, unggas hidup (itik dan ayam pedaging) yang berada dalam kandang penampungan sementara merupakan potensial penyebaran virus AI ke lingkungannya

Reaction-diffusion systems with constant diffusivities: conditional symmetries and form-preserving transformations

Q-conditional symmetries (nonclassical symmetries) for a general class of two-component reaction-diffusion systems with constant diffusivities are studied. Using the recently introduced notion of Q-conditional symmetries of the first type (R. Cherniha J. Phys. A: Math. Theor., 2010. vol. 43., 405207), an exhaustive list of reaction-diffusion systems admitting such symmetry is derived. The form-preserving transformations for this class of systems are constructed and it is shown that this list contains only non-equivalent systems. The obtained symmetries permit to reduce the reaction-diffusion systems under study to two-dimensional systems of ordinary differential equations and to find exact solutions. As a non-trivial example, multiparameter families of exact solutions are explicitly constructed for two nonlinear reaction-diffusion systems. A possible interpretation to a biologically motivated model is presented

Understanding Terrorist Organizations with a Dynamic Model

Terrorist organizations change over time because of processes such as recruitment and training as well as counter-terrorism (CT) measures, but the effects of these processes are typically studied qualitatively and in separation from each other. Seeking a more quantitative and integrated understanding, we constructed a simple dynamic model where equations describe how these processes change an organization's membership. Analysis of the model yields a number of intuitive as well as novel findings. Most importantly it becomes possible to predict whether counter-terrorism measures would be sufficient to defeat the organization. Furthermore, we can prove in general that an organization would collapse if its strength and its pool of foot soldiers decline simultaneously. In contrast, a simultaneous decline in its strength and its pool of leaders is often insufficient and short-termed. These results and other like them demonstrate the great potential of dynamic models for informing terrorism scholarship and counter-terrorism policy making.Comment: To appear as Springer Lecture Notes in Computer Science v2: vectorized 4 figures, fixed two typos, more detailed bibliograph

The ratio of soluble fms–like tyrosine kinase 1 to placental growth factor predicts time to delivery and mode of birth in patients with suspected preeclampsia- a secondary analysis of the INSPIRE trial

Background: The ratio of soluble fms–like tyrosine kinase 1 to placental growth factor (sFLT1/PLGF) is a useful biomarker for preeclampsia. Since it is a measure of placental dysfunction, it could also be a predictor of clinical deterioration and fetal tolerance to intrapartum stress. Objectives: We tested the hypothesis that sFLT1/PLGF ratio predicts time to delivery. Secondary objectives were to examine associations between the sFLT1/PLGF ratio and mode of birth, fetal distress, need for labor induction and birthweight z-score. Study design: Secondary analysis of the INSPIRE trial, a randomized interventional study on prediction of preeclampsia/eclampsia in which women with suspected preeclampsia were recruited and their blood sFLT1/PLGF ratio was assessed. We stratified participants into three groups according to the ratio result: category 1 (sFLT1/PLGF≤38); category 2 (sFLT1/PLGF>38 and <85); and category 3 (sFLT1/PLGF≥85). We modelled time from sFLT1/PLGF determination to delivery using Kaplan-Meier curves and compared the three ratio categories adjusting for gestational age at sFLT1/PLGF determination and trial arm with Cox Regression. The association between ratio category and mode of delivery, induction of labour and fetal distress was assessed using a multivariable logistic regression adjusting for gestational age at sampling and trial arm. The association between birthweight z-score and sFLT1/PLGF ratio was evaluated using multiple linear regression. Subgroup analysis was conducted in women with no preeclampsia and spontaneous onset of labor; women with preeclampsia; and participants in the non-reveal arm. Results: Higher ratio categories were associated with a shorter latency from sFLT1/PLGF determination to delivery (37 vs 13 vs 10 days for ratios categories 1-3 respectively), hazards ratio for category 3 ratio of 5.64 (95%CI 4.06-7.84, p<0.001). A sFLT/PlGF ratio≥85 had specificity of 92.7%(95%CI 89.0-95.1%) and sensitivity of 54.72% (95% CI, 41.3-69.5) for prediction of preeclampsia indicated delivery within 2 weeks. A ratio category 3 was also associated with decreased odds of spontaneous vaginal delivery (OR 0.47, 95%CI 0.25-0.89); an almost six fold increased risk of emergency cesarean section (OR 5.89, 95%CI 3.05-11.21); and a three-fold increased risk for intrapartum fetal distress requiring operative delivery or cesarean section (OR 3.04, 95%CI 1.53-6.05) when compared to patients with ratios≤38. Higher ratio categories were also associated with higher odds of induction of labor when compared to ratios category 1 (category 2, OR 2.20, 95%CI 1.02-4.76; category 3, OR 6.0, 95%CI 2.01-17.93); and lower median birthweight z-score. Within subgroups of women a)without preeclampsia and with spontaneous onset of labor and b)women with preeclampsia, the log ratio was significantly higher in patients requiring intervention for fetal distress or failure to progress compared to those who delivered vaginaly without intervention. In the subset of women with no preeclampsia and spontaneous onset of labour, those who required intervention for fetal distress or failure to progress had a significantly higher log ratio than those who delivered vaginaly without needing intervention. Conclusion: The sFLT1/PLGF ratio might be helpful in risk-stratification of patients who present with suspected preeclampsia regarding clinical deterioration, intrapartum fetal distress and mode of birth (including the need for intervention in labour)