Fetal heart rate mirrors maternal temperature during posterior fossa craniotomy: a case report.

While it is well known that maternal temperature affects fetal heart rate, the exact relationship is not well described. The circumstances accompanying most cases of maternal hypothermia and rewarming (e.g. a drowning event) have precluded a precise quantitative description of this relationship. We describe hypothermia and controlled rewarming during resection of a maternal brain stem tumor in the early third trimester. Continuous electronic fetal heart rate and core temperature monitoring demonstrated a near linear relationship during the development of hypothermia and rewarming. Recognition of the close relationship between maternal temperature and fetal heart rate can help safeguard maternal and fetal health, and prevent unnecessary delivery during non-obstetric surgery in pregnancy.

pCONUS 2 and pCONUS 2-HPC for the treatment of wide-necked intracranial aneurysms: Periprocedural, 6-month, and early 2-year follow-up outcomes.

BACKGROUND/PURPOSE: pCONUS 2 and pCONUS 2-HPC are novel neck-bridging devices designed to support endovascular coil occlusion of wide-necked intracranial bifurcation aneurysms. This study summarises periprocedural outcomes, 6-month, and early 2-year follow-up results following its introduction in an interventional neuroradiology centre. MATERIALS/METHODS: This prospective, single-arm study assessed 20 aneurysms treated over a 40 month time period from time of procedure to 2 years post-procedure. Data collected included patient demographics, aneurysm features, and intraprocedural, 6-month, and 2-year post-procedural complications and angiographic features. RESULTS: The mean age of the cohort was 59+-SD 7.7 years. 16 unruptured aneurysms were treated (pCONUS 2 13/16, pCONUS 2-HPC 3/16) and 4 ruptured aneurysms were treated with pCONUS 2-HPC. Unruptured cases received dual antiplatelet therapy pre- and post-procedure while ruptured cases received single antiplatelet therapy. 9/20 aneurysms were located at the MCA bifurcation and 7/20 at the basilar tip. The remaining 4 aneurysms were at various bifurcations in the anterior circulation. 11/20 were small (<10mm) and 9/20 were large (10-25mm). There was one periprocedural complication: a retroperitoneal bleed. There were no post-procedural intracranial complications or at 6-months follow-up. At 6 months, satisfactory occlusion was achieved in 94% of cases (15/16). There was one delayed death at 2-year follow-up from an unrelated cause. CONCLUSION: pCONUS 2 and pCONUS 2-HPC have excellent short and medium-term safety profiles and clinical outcomes with no procedure-related mortality or morbidity and good occlusion rates at 6-month follow-up. The use of pCONUS 2-HPC with single antiplatelet therapy is feasible and did not cause any complications.

Mechanical thrombectomy in acute ischaemic stroke: a review of the different techniques.

Endovascular mechanical thrombectomy (MT) is reserved for acute ischaemic stroke secondary to large vessel occlusion. The various MT techniques employed in the treatment of hyperacute strokes are constantly evolving with new devices and improvisation of existing technology (Wahlgren, et al 2016). In this review, we describe a variety of MT techniques gained from our experience of performing over 350 procedures in 7 years of providing a 24/7 service within the national framework of a hyperacute stroke centre. We outline a number of endovascular techniques, procedure limitations, and potential complications.

Implementation of a split-bolus single-pass CT protocol at a UK major trauma centre to reduce excess radiation dose in trauma pan-CT.

AIM: To quantify the dose reduction and ensure that the use of a split-bolus protocol provided sufficient vascular enhancement. MATERIALS AND METHODS: Between 1 January 2014 and 31 May 2014, both split bolus and traditional two-phase scans were performed on a single CT scanner (SOMATOM Definition AS+, Siemens Healthcare) using a two-pump injector (Medrad Stellant). Both protocols used Siemens' proprietary tube current and tube voltage modulation techniques (CARE dose and CARE kV). The protocols were compared retrospectively to assess the dose-length product (DLP), aortic radiodensity at the level of the coeliac axis and radiodensity of the portal vein. RESULTS: There were 151 trauma CT examinations during this period. Seventy-eight used the split-bolus protocol. Seventy-one had traditional two-phase imaging. One patient was excluded as they were under the age of 18 years. The radiodensity measurements for the portal vein were significantly higher (p<0.001) in the split-bolus protocol. The mean aortic enhancement in both protocols exceeded 250 HU, although the traditional two-phase protocol gave greater arterial enhancement (p<0.001) than the split-bolus protocol. The split-bolus protocol had a significantly lower (p<0.001) DLP with 43.5% reduction in the mean DLP compared to the traditional protocol. CONCLUSION: Split-bolus CT imaging offers significant dose reduction for this relatively young population while retaining both arterial and venous enhancement.

Glutamic acid decarboxylase (anti-GAD) & tissue transglutaminase (anti-TTG) antibodies in patients with thyroid autoimmunity.

BACKGROUND & OBJECTIVES: Several autoimmune disorders have been reported to be associated with autoimmune thyroiditis and may coexist with other organ-specific autoantibodies. The aim of the present study was to evaluate the presence of tissue transglutaminase (anti-TTG) and glutamic acid decarboxylase (anti-GAD) antibodies in patients suffering from autoimmune thyroiditis as diagnosed by anti-thyroid peroxidase (anti-TPO) antibodies, which may indicate high risk for developing celiac disease or type 1 diabetes mellitus. METHODS: Five thousand children and 2800 adults were screening as part of a general health examination done on a voluntary basis in four different parts of Delhi. A total of 577 subjects positive for anti-TPO antibody constituted the cases. Equal number of age and sex matched anti-TPO antibody negative controls were randomly selected from the same cohort to form paired case control study. The cases and controls were further divided into two groups as follows: group-1 (children and adolescent <18 yr), group-2 (adults >18 yr). Serum samples of cases and controls were analysed for thyroid function test (FT3, FT4, and TSH), anti-TTG and anti-GAD antibodies. RESULTS: A total of 1154 subjects (577 cases and 577 controls) were included in this study. Hypothyroidism was present in 40.2 per cent (232) cases compared to only 4.7 per cent (27) in controls (P<0.001). Anti-TTG and anti-GAD antibodies were present in 6.9 and 12.5 per cent subjects among cases compared to 3.5 per cent (P=0.015) and 4.3 per cent (P=0.001) in controls, respectively. Only anti-GAD antibody were significantly positive in cases among children and adolescents (P =0.0044) and adult (P=0.001) compared to controls. Levels of anti-TTG and anti-GAD antibodies increased with increasing titre of anti-TPO antibody. INTERPRETATION & CONCLUSIONS: Our findings showed high positivity of anti-GAD and anti-TTG antibodies among subjects with thyroid autoimmunity. It is, therefore, important to have high clinical index of suspicion for celiac disease or type 1 diabetes mellitus in patients with autoimmune thyroiditis.

Percentage body fat in apparently healthy school children from northern India.

CONTEXT: Increased prevalence of obesity in childhood and adolescence, defined by the use of body mass index (BMI), has drawn attention towards direct measurement of body fat. OBJECTIVE: To develop age-and sex-specific reference distribution of body fat in apparently healthy North-Indian children in the age group of 7-17 years and to assess agreement between obesity (defined by BMI) and excess body fat. DESIGN: Study subjects for this cross sectional study included 1640 apparently healthy school children (825 boys; 815 girls) aged 7-17 years. Total body fat was measured by dual energy X-rays absorptiometry (DXA). The excess body fat by DXA was defined by two methods, prevalence matching and with the use of 85th and 95th centile cutoffs. RESULTS: The mean ± SD, 3rd, 10th, 25th, 50th, 75th, 90th and 97th centile values of percentage body fat (PBF) are presented. PBF was highly correlated with BMI in both boys and girls (all boys: r=0.76, P<0.0001; all girls r=0.81, P<0.0001). There was no significant difference noted in PBF between boys and girls at the age of 7-8 years. From 9 years onwards, girls had significantly higher PBF than boys. Moderate degree of agreement was observed between BMI and PBF by DXA by both methods. CONCLUSIONS: Smoothened reference distribution of PBF for North-Indian children and adolescents in Delhi are provided. Indian children accumulate more body fat during peri-pubertal years in comparison with US children.

Dyslipidemia in subclinical hypothyroidism in an Indian population.

OBJECTIVES: In view of inconsistent reports on the prevalence of dyslipidemia in subclinical hypothyroidism (SCH), we studied lipid abnormalities in Indian subjects with SCH. DESIGN AND METHODS: A cross sectional study of 5343 subjects divided in two groups, Group-1 (age≤18 years) and Group-2 (age>18 years) was undertaken. They were further subdivided on the basis of their thyroid functional status: Normal (Control); SCH with TSH≤10.0mIU/L (SCH-1); and SCH with TSH>10mIU/L (SCH-2). RESULTS: Prevalence of SCH was 14.7%. The only lipid abnormality in children and adolescents was low HDL in subjects with TSH>10mIU/L compared with controls. Serum total cholesterol (TC), and LDL cholesterol (LDL) were significantly higher in adults with TSH>10mIU/L compared to controls. There were no significant changes in lipid parameters in subjects with SCH having TSH≤10.0mIU/L, compared to controls. Serum TSH was positively and FT3 and FT4 were negatively correlated with TC and LDL. CONCLUSIONS: Atherogenic lipid abnormalities were observed in adult subjects with SCH-2 (TSH>10.0mIU/L), and not in subjects with SCH-1 who had TSH≤10.0mIU/L in Indian population.

Bone health in healthy Indian population aged 50 years and above.

UNLABELLED: One thousand six hundred healthy subjects aged more than 50 years, residing in Delhi, were evaluated for bone mineral metabolic parameters. High prevalence of osteoporosis (35.1% subjects) was observed in this population. Bone mineral density (BMD) correlated positively with body mass index (BMI) and negatively with PTH levels. No correlation was observed with serum 25(OH)D levels. INTRODUCTION: To assess the bone health status in elderly Indians and compare peripheral DXA (pDXA) with central DXA in evaluation of osteoporosis. METHODS: The study involved 1,600 healthy subjects more than 50 years of age residing in Delhi, India, who underwent anthropometric, biochemical, and hormonal evaluation. BMD was measured by DXA at lumbar spine, hip, and distal radius; and by pDXA at forearm and calcaneum. RESULTS: Seven hundred ninety-two males and 808 postmenopausal females, with a mean age of 57.67 ± 9.46 years were evaluated. Osteoporosis was present in 35.1% subjects (M-24.6%, F-42.5%) and osteopenia in 49.5% (M-54.3%, F-44.9%). Prevalence of osteoporosis increased with age in females, but not in males. BMD at all sites, except distal radius, was positively correlated with BMI (r=0.037, p=0.14). Total body BMD was negatively correlated with alkaline phosphatase (r= -0.184, p<0.00001) and PTH levels (r= -0.099, p<0.00001), respectively. No significant correlation was observed between serum 25(OH)D levels and BMD at any site. BMD at forearm and calcaneum, measured using pDXA, showed strong positive correlation with BMD measured by central DXA. pDXA had sensitivity of 88%, specificity of 55%, and negative and positive predictive values of 89% and 52%, respectively, at T-score -2.5 at peripheral sites compared to central DXA. CONCLUSIONS: A high prevalence of osteoporosis was observed in elderly Indian subjects. pDXA has high negative predictive value, making it a useful tool in population screening for osteoporosis.

Vitamin D status in healthy Indians aged 50 years and above.

INTRODUCTION: There is widespread prevalence of vitamin D deficiency from new-born to infancy, childhood and adult male and females (non-pregnant, pregnant and lactating). However, there is limited information of the vitamin D status in elderly Indians. MATERIAL AND METHODS: The study was carried in 1346 healthy subjects more than 50 years of age residing in Delhi, India. These subjects, who were divided in two groups: Group-1 (50-< 65 years) and Group-2 (> or = 65 years), underwent anthropometric, biochemical and hormonal evaluation for vitamin D status Bone mineral density was measured by dual X-ray absorptiometry. RESULTS: There were 643 males and 703 females, with a mean age of 58.0 +/- 9.5 years (range 50-84 years). Vitamin D deficiency [VDD, serum 25(OH)D levels < 20 ng/ml) was present in 1228 (91.2%) and Vitamin D insufficiency [VDI, serum 25(OH)D levels 20-< 30 ng/ml] in 92 (6.8%). There was no significant difference in prevalence of either VDD or VDI between two age groups and sexes. Serum 25(OH)D levels were negatively correlated with PTH levels (r -0.027, p <0.00001) and BMI (r -0.128, p 0.05). Prevalence of secondary hyperparathyroidism increased from 14.1% to 43.1% from VDI to severe VDD. PTH levels started rising at vitamin D level < 30 ng/ml. However, more than 50% of subjects with severe VDD had PTH levels within normal range. High prevalence of osteopenia (50.2%) and osteoporosis (31.2%) was observed in this population. CONCLUSION: Hypovitaminosis D is universal above the age of 50 years in north India. Absence of a PTH response was observed in more than 50% of individuals with VDD, the cause of which merits further evaluation. Normal bone mass was observed in only 18.6% of study subjects.

Reference intervals of serum calcium, ionized calcium, phosphate and alkaline phosphatase in healthy Indian school children and adolescents.

OBJECTIVE: To develop age- and sex-specific reference interval of serum total calcium, ionized calcium, inorganic phosphates and alkaline phosphatase in healthy Indian children in the age group of 6-17 years. DESIGN AND METHOD: Subjects for this study were selected from the schools of Delhi. The final analysis included 3,327 children in the age group of 6-17 years (1707 boys; 1620 girls). RESULTS: The mean, standard deviation, 5th, 25th, 50th, 75th, 90th, 95th and 97th centile values of biochemical parameters for boys and girls are presented. All these parameters were significantly higher in boys than girls except serum ionized calcium. Serum total calcium (r -0.1362, p<0.001), serum inorganic phosphate (r -0.45, p<0.001) and serum alkaline phosphatase (r -0.5587, p<0.001) have shown inverse relationship with age. CONCLUSIONS: Reference interval of selected biochemical parameters for healthy Asian-Indian children in the age group of 6-17 years is presented.

Vitamin D nutritional status of exclusively breast fed infants and their mothers.

BACKGROUND: Vitamin D nutrition has a profound effect on the development of an infant. Vitamin D status of mothers and their infants are closely correlated. While hypovitaminosis D has emerged as a significant public health problem across all age groups, there is limited information of this condition in lactating mothers and their breast fed infants. AIM: To evaluate the vitamin D status of lactating mothers and their breast fed infants. SUBJECTS AND METHODS: 180 healthy lactating mothers and exclusively breast fed infants, 2-24 weeks old, were recruited for the study. The mother-infant pairs underwent concurrent clinical, biochemical and hormonal evaluation for calcium-vitamin D-PTH axis. RESULTS: The mean serum 25(OH)D values in lactating mothers was 27.2 +/- 14.6 nmol/l (10.9 +/- 5.8 ng/ml), while that of their infants was 28.9 +/- 20.8 nmol/l (11.6 +/- 8.3 ng/ml). Serum 25(OH)D levels <25 nmol/l (10 ng/ml) were found in 47.8% of the mothers and 43.2% of the infants. Among these, elevated PTH levels (>54 pg/ml) were seen in 59.3% of the mothers and 69.6% of the infants. A highly significant negative correlation was found between serum 25(OH)D and PTH in mothers (r = -0.480, p = 0.01) and their infants (r = -0.431, p = 0.01). A strong positive correlation was seen of 25(OH)D levels in mother-infant pairs (r = 0.324, p = 0.001). CONCLUSIONS: A high prevalence of vitamin D deficiency was found in lactating mothers and their exclusively breast fed infants. Infants born to mothers with hypovitaminosis D had 3.8 times higher risk of developing hypovitaminosis D as compared to those born to mothers with normal vitamin D levels.

Reflux and sleeping disorders: a systematic review.

INTRODUCTION: Laryngopharyngeal reflux is perhaps the most extensively researched laryngology topic of the last decade. It has been suggested that some supraoesophageal symptoms, most notably asthma and laryngospasm, may be associated with night-time, or supine, reflux. The aim of this review was to assess the levels of evidence regarding a correlation between night-time reflux, snoring and apnoea. METHODS: A Medline search was performed using the terms 'reflux', 'night-time', 'larynx', 'gastroesophageal', 'laryngopharyngeal', 'sleep', 'apnoea', 'snoring' and 'ear nose throat'. The retrieved literature was reviewed, focusing on randomised and non-randomised, controlled, prospective trials. Papers on both paediatric and adult populations were included. Non-English language papers were excluded. RESULTS: We found no randomised, controlled trials or meta-analyses addressing the possible correlation between reflux and snoring and/or apnoea. CONCLUSIONS: The role of night-time reflux in paediatric and adult snoring and apnoea is well described in the literature, but is based on poor levels of evidence from uncontrolled studies and case reports.

Comparison of clinical and histopathological evaluation of tonsils in pediatric and adult patients.

The aim of this study was to determine clinical features that could predict the presence of tonsillar malignancy in children and adults. A retrospective review of the histopathologic reports of the children, who underwent tonsillectomy (753 cases) during the past 16 years (January 1991-December 2006) in a busy district general hospital, was undertaken. We compared the results to the pre-operative data of the patients, for risk factors of malignancy. Such proposed risk factors were tonsillar asymmetry, palpable firmness, visible lesions, neck adenopathy, history of malignancy, and systemic symptoms. The same data (history, risk factors and histopathologic results) were reviewed for an adult group (>16 years old, 1,027 cases) who underwent tonsillectomy during that period, and the results of the two groups were compared. In the pediatric group only one case was diagnosed as lymphoma (0.13%) and the rest as chronic inflammation (47%), reactive tonsil tissue (26%), lymphoid hyperplasia (19%) and actinomycosis (8%). In the lymphoma case, the diagnosis was suspected preoperatively by history and clinical manifestations. In the adult group, there were 21 cases of malignancy out of 1,027 cases (2.04%), again with one or more positive risk factors in the pre-surgery history. Based on our review, it is concluded that histopathology of tonsillectomy is not necessary in children unless there is clinical suspicion based on preoperative findings. A protocol based on proposed risk factors which may be predictive of possible malignancy can be used as a guide to intraoperative histology.

Bulimia and oesophageal foreign bodies.

OBJECTIVES: To demonstrate the importance of a detailed history when assessing patients with a repeated pattern of foreign body ingestion. CASE REPORT: A 19-year-old woman presented to our department following accidental ingestion of a teaspoon. On further questioning, she admitted to a habit of binge-eating followed by self-induced vomiting, in order to avoid weight gain; she blamed this behaviour on a stressful relationship with her partner. She also had one previous episode of accidental ingestion of a plastic spoon, which had been removed by oesophagogastroduodenoscopy. The patient underwent an uneventful rigid oesophagoscopy and foreign body removal. During post-operative recovery, she admitted that she had suffered for years with bulimia and anorexia nervosa. She was discharged home after appropriate psychiatric counselling, and follow up was arranged. CONCLUSIONS: Oesophageal foreign bodies are commonly encountered in otolaryngology practice. Such circumstances are often compounded by pre-existing psychiatric problems such as bulimia and/or anorexia nervosa. Patients with bulimia may often present with a very similar pattern of multiple episodes of ingestion of large foreign bodies. Identification of this eating disorder (especially when there is a recurrent history of large, accidentally ingested foreign bodies) and prompt psychiatric referral is essential for efficient long-term management of this condition.

Establishment of reference range for thyroid hormones in normal pregnant Indian women.

BACKGROUND: Interpretation of thyroid function tests during pregnancy needs trimester-related reference intervals from pregnant populations with minimal risk for thyroid dysfunction. While India has become iodine sufficient after two decades of salt iodisation, there is no normative data for thyroid function from healthy pregnant women of this country. AIMS AND OBJECTIVES: To determine trimester-specific reference ranges for free triiodothyronine (FT(3)), free thyroxine (FT(4)) and thyrotropin (TSH) from healthy pregnant Indian women. DESIGN: Cross-sectional study in a reference population of pregnant women. SETTING: Primary care level obstetric department in India. POPULATION: Women with uncomplicated pregnancy in any trimester. METHODS: Five hundred and forty-one apparently healthy pregnant women with uncomplicated single intrauterine gestations reporting to the Armed Forces Clinic in any trimester were consecutively recruited. Clinical examination, thyroid ultrasound for echogenicity and nodularity and estimation of FT(3), FT(4), TSH and antithyroid antibodies (antithyroperoxidase [anti-TPO] and antithyroglobulin [anti-Tg]) using electrochemiluminescence technique were carried out. From this entire sample, a disease- and risk-free reference population was obtained by excluding those with any known factor that could affect thyroid function or those who were being treated for thyroid dysfunction. MAIN OUTCOME MEASURE: None. RESULTS: Of the 541 consecutive pregnant women in different trimesters enrolled for the study, 210 women were excluded. The composition of reference population comprising 331 women was 107 in first trimester, 137 in second trimester and 87 in third trimester. The 5th and 95th percentiles values were used to determine the reference ranges for FT(3), FT(4) and TSH. The trimester-wise values in the first, second and third trimesters were: FT(3) (1.92-5.86, 3.2-5.73 and 3.3-5.18 pM/l), FT(4) (12-19.45, 9.48-19.58 and 11.32-17.7 pM/l) and TSH (0.6-5.0, 0.44-5.78 and 0.74-5.7 iu/ml), respectively. Analysis of mean, median values for FT(3), FT(4) and TSH between each trimester showed no significant difference in FT(3) and TSH values (95% CI). However, FT(4) showed significant variation between trimesters with values decreasing with advancing gestational age (P value: first versus second = 0.015, first versus third = 0.003 and second versus third = not significant). Women with antibody positivity and hypoechogenicity of thyroid gland had significantly higher TSH values when compared with women with antibody negativity and normoechogenicity. CONCLUSIONS: Reference ranges of FT(3), FT(4) and TSH have been established for pregnant Indian women using 5th and 95th percentiles.

Pott's puffy tumor following an insect bite.

Pott's puffy tumor, a feature of osteomyelitis of the frontal bone, is a rare entity, especially in adults. Sir Percival Pott originally described this condition as a complication of trauma to the frontal bone. This is also a recognized complication of fronto-ethmoidal sinusitis. We present a rare case of Pott's puffy tumor caused by an insect bite presenting initially as a preseptal cellulitis and explore its pathogenesis and management.

Modeling percolation in high-aspect-ratio fiber systems. I. Soft-core versus hard-core models.

Numerical and analytical studies of the onset of percolation in high-aspect-ratio fiber fiber systems such as nanotube reinforced polymers available in the literature have consistently modeled fibers as penetrable, straight, capped cylinders, also referred to as spherocylinders. In reality, however, fibers of very high-aspect ratio embedded in a polymer do not come into direct physical contact with each other, let alone exhibit any degree of penetrability. Further, embedded fibers of very high-aspect ratio are often actually wavy, rather than straight. In this two-part paper we address these critical differences between known physical systems, and the presently used spherocylinder percolation model. In Paper I we evaluate the effect of allowing penetration of the model fibers on simulation results by comparing the soft-core and the hard-core approaches to modeling percolation onset. We use Monte Carlo simulations to investigate the relationship between percolation threshold and excluded volume for both modeling approaches. Our results show that the generally accepted inverse proportionality between percolation threshold and excluded volume holds for both models. We further demonstrate that the error introduced by allowing the fibers to intersect is non-negligible, and is a function of both aspect ratio and tunneling distance. Thus while the results of both the soft-core model and hard-core assumptions can be matched to select experimental results, the hard-core model is more appropriate for modeling percolation in nanotubes-reinforced composites. The hard-core model can also potentially be used as a tool in calculating the tunneling distance in composite materials, given the fiber morphology and experimentally derived electrical percolation threshold. In Paper II we investigate the effect of the waviness of the fibers on the onset of percolation in fiber reinforced composites.

Modeling percolation in high-aspect-ratio fiber systems. II. The effect of waviness on the percolation onset.

The onset of electrical percolation in nanotube-reinforced composites is often modeled by considering the geometric percolation of a system of penetrable, straight, rigid, capped cylinders, or spherocylinders, despite the fact that embedded nanotubes are not straight and do not penetrate one another. In Part I of this work we investigated the applicability of the soft-core model to the present problem, and concluded that the hard-core approach is more appropriate for modeling electrical percolation onset in nanotube-reinforced composites and other high-aspect-ratio fiber systems. In Part II, we investigate the effect of fiber waviness on percolation onset. Previously, we studied extensively the effect of joint morphology and waviness in two-dimensional nanotube networks. In this work, we present the results of Monte Carlo simulations studying the effect of waviness on the percolation threshold of randomly oriented fibers in three dimensions. The excluded volumes of fibers were found numerically, and relationships between these and percolation thresholds for two different fiber morphologies were found. We build on the work of Part I, and extend the results of our soft-core, wavy fiber simulations to develop an analytical solution using the more relevant hard-core model. Our results show that for high- aspect-ratio fibers, the generally accepted inverse proportionality between percolation threshold and excluded volume holds, independent of fiber waviness. This suggests that, given an expression for excluded volume, an analytical solution can be derived to identify the percolation threshold of a system of high-aspect-ratio fibers, including nanotube-reinforced composites. Further, we show that for high aspect ratios, the percolation threshold of the wavy fiber networks is directly proportional to the analytical straight fiber solution and that the constant of proportionality is a function of the nanotube waviness only. Thus the onset of percolation can be adequately modeled by applying a factor based on fiber geometry to the analytical straight fiber solution.

Direct stochastic simulation of Ca2+ motion in Xenopus eggs.

The release of important intracellular ions has been widely modeled using two approaches, namely, (1) Fickian diffusion, in which sometimes tensorial diffusion coefficients are used to fit observed temporally varying concentrations of calcium, and (2) cellular automata, which produce a set of localized finite difference equations that result in complex global behavior. Here, we take a different approach, employing some assumed, a priori, distribution of ion-binding proteins in the cell, and some assumed biochemical capture and release characteristics to explain ionic motion, and ultimately, distribution. We study several scenarios for ion distribution, based on differences in binder action and distribution. The numbers and strengths of ion binders, spatial variation in inositol 1,4,5-triphosphate concentration, together with the escalating distribution of ionic diffusion speed, are found to be key factors leading to concavity in the Ca2+ wave shape. We also offer an explanation for geometrical effects on previously observed ion diffusion speeds in the cellular cortex of the Xenopus laevis egg during fertilization, based on an angle-of-view correction.