Combining Molecular Dynamics and Monte Carlo Simulations to Model Chemical Vapor Deposition: Application to Diamond

Gas-surface reactions of the type that contribute to growth during the chemical vapor deposition (CVD) of diamond films are generally completed in picoseconds, well within timescales accessible by molecular dynamics (MD) simulations. For low-pressure deposition, however, the time between collisions for a surface site can be microseconds, which makes direct modeling of CVD crystal growth impossible using standard MD methods. To effectively bridge this discrepancy in timescales, the gas-surface reactions can be modeled using MD trajectories, and then this data can be used to define probabilities in a Monte Carlo algorithm where each step represents a gas-surface collision. We illustrate this approach using the reaction of atomic hydrogen with a diamond (111) surface as an example, where we use abstraction and sticking probabilities generated using classical trajectories in a simple Monte Carlo algorithm to determine the number of open sites as a function of temperature. We also include models for the thermal desorption of hydrogen that predict that growth temperatures are not restricted by the thermal loss of chemisorbed hydrogen.

Concentration effect on tuning of block copolymer-mediated synthesis of gold nanoparticles

Synthesis of gold nanoparticles has been examined using triblock copolymer Pluronic P85 (EO26PO39EO26) at different concentrations as a function of hydrogen tetrachloroaureate (III) hydrate (HAuCl4 x 3H2O) in aqueous solution. The concentration of P85 block copolymer was varied from 0.5 to 2 wt% at fixed temperature (30 degrees C) in presence of HAuCl4 x 3H2O in the range of 0.002 to 0.2 wt% for each P85 concentration. The surface plasmon resonance in the time-dependent UV-visible spectra reveals that increase in the block copolymer concentration increases the yield of the gold nanoparticles but decreases their stability. Both small-angle neutron scattering (SANS) and dynamic light scattering (DLS) show that the number density of block copolymer micelles increase almost linearly with the concentration, which is related to result in higher numbers of nucleation centers and therefore increase in the yield of gold nanoparticles. The fact that increase in the number density of nanoparticles also increases the chances of aggregation and this tends to decrease the stability at higher block copolymer concentration. Transmission electron microscopy (TEM) images confirm the larger sizes of the nanoparticles formed in these systems at higher concentrations.

Temporal trends in cause-specific late mortality among five-year survivors of childhood cancer

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Background: Five-year survival rates for childhood cancer have increased over the past 4 decades, increasing the number of long-term survivors. Among 5-yr survivors, the impact of changes in therapy on cause-specific late mortality has not been thoroughly assessed. Methods: Late mortality was evaluated over 3 eras (1974–81, 1982–90, 1991–2000) in 26,643 5-year survivors diagnosed <21 years of age from the SEER population-based registry. Cause-specific mortality was categorized as death from recurrence/progression of primary disease, external causes, and non-recurrence/non-external causes (Non-Recur/Ext) (i.e., deaths from health conditions including sequelae of cancer therapy). Results: All-cause and Recurrence mortality was significantly lower in more recent eras ( Table ). No significant improvement in late mortality attributable to Non-Recur/Ext causes was seen. Additionally, all-cause mortality was significantly lower in more recent eras for 5-year survivors of ALL, AML, Hodgkin, NHL, and CNS tumors, but not neuroblastoma and Ewing's Sarcoma where an increase in cumulative incidence of late mortality was seen in more recent eras. Significant improvement in late mortality from Recurrence by era was seen in most diagnostic groups. Conclusions: All-cause late mortality has improved with more recent eras, attributable to reduced rates of mortality from progression of primary disease (i.e., durable remission). Importantly, however, efforts to reduce the toxicity of more recent therapies have not produced detectable reduction in mortality attributable to other health conditions including sequelae of cancer therapy (non-Recur/Ext causes of death), which would include death from second malignancy, cardiac and pulmonary conditions. Worsening late mortality for 5-year survivors of neuroblastoma and Ewing's sarcoma may be due to improved use of salvage therapies that delay, but do not ultimately prevent death. [Table: see text]

No significant financial relationships to disclose.

Preoperative evaluation of epithelial ovarian cancer with multidetector computed tomography and its correlation with surgical outcome

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Background: In the management of epithelial ovarian cancer (EOC), optimum debulking surgery (residual tumour of 1 cm or less) is the most important prognostic factor and is associated with higher survival We conducted a prospective study to evaluate the role of Multidetector (MD) CT scan to predict optimal debulking in advanced EOC. Methods: Between December, 2004 and October, 2006, 38 previously untreated patients (median age-50 years, range 26 to 70) were evaluated with contrast- enhanced MD CT scan of abdomen and pelvis. All CT scans were performed on four-slice MD CT scanner with thin slice image acquisition. Multiplanar coronal, sagital or oblique images were constructed and all images were reviewed by at least 2 radiologists. The extent of disease was determined and mapped for all areas of abdomen and pelvis. Patients underwent primary debulking surgery in which total abdominal hysterectomy, bilateral salphingo-oophorectomy, omentectomy and optimal cytoreduction was done. CT scan films were reviewed and compared with surgical findings. A CT scan scoring system was developed to predict the optimum debulking using 10 parameters: ascites, pelvic, peritoneal deposits, large bowel, small bowel, omentum, diaphragm, liver, lymphadenopathy and lesser sac. Each factor was assigned a score of 0 to 2. The statistical analysis was done using SPSS version 11 and EpiInfo 6 software. Results: The mean interval between CT scan and surgery was 11 days. 18 of 38 patients had a CT score = 7; all 18 had sub-optimal debulking. Of remaining 20 patients with CT score <7, 17(44.7%) had optimum and 3 had sub-optimal cytoreduction. The sensitivity and specificity was 85.7% (95% CI 62.6–96.2) and 100% (95% CI 77.1–100), respectively. It had positive predictive value of 100% and negative predictive value of 85% with accuracy of 92% in identification of patients who would not benefit from surgery. Presence of tumor at gall bladder fossa, porta hepatis, ligament teres, spleen , stomach, pancreas, lesser sack and pelvic side walls was associated with sub-optimal debulking. Conclusions: Pre-operative CT scan scoring helps to identify patients who are likely to have sub-optimal debulking and may be candidates for neoadjuvant chemotherapy

No significant financial relationships to disclose.

Skeletal stability after correction of maxillary hypoplasia by the Glasgow extra-oral distraction (GED) device

Maxillary distraction osteogenesis delivers excellent results, particularly in patients with clefts. In the past, devices such as the conventional facemask and the rigid external distraction device have been used to correct maxillary hypoplasia after a Le Fort I osteotomy. We describe a new device, the Glasgow extra-oral distraction device. The extent of skeletal and dental stability of corrections achieved in 10 patients with maxillary hypoplasia associated with clefts was satisfactory. This device costs little, can be produced in developing countries, and provides effective treatment for severe secondary deformity associated with clefts.

Irradiation-induced magnetism in carbon nanostructures

Nitrogen (15N) and carbon (12C) ion implantations with implant energy of 100 keV for different doses were performed on nanosized diamond (ND) particles. Magnetic measurements on the doped ND show ferromagnetic hysteresis behavior at room temperature. The saturation magnetization (M(s)) in the case of 15N implanted samples was found to be higher compared to the 12C implanted samples for dose sizes greater than 10(14) cm(-2). The role of structural modification or defects along with the carbon-nitrogen (C-N) bonding states for the observed enhanced ferromagnetic ordering in 15N doped samples is explained on the basis of x-ray photoelectron spectroscopy measurements.

Vibrational characteristics of carbon nanotubes as nanomechanical resonators

Using eigenvalue analysis of mass and stiffness matrices directly computed from atomistic simulations, natural frequencies and mode shapes of various carbon nanotubes are studied. The stiffness matrix was developed from the Tersoff-Brenner potential for carbon-carbon interactions. The computed frequencies of the radial breathing modes of a variety of armchair (n, n) nanotubes agree well with results obtained by others using different techniques. In addition, the study reveals diverse mode shapes such as accordion-like axial modes, lateral bending modes, torsional modes, axial shear modes, and radial breathing modes for a variety of single-wall, multi-wall, and bamboo-type carbon nanotubes. The effects of different constraints on the carbon nanotube ends on the computed frequencies and mode shapes have been investigated for possible applications in vibration sensors or electromechanical resonators.

Molecular mechanisms of ventricular hypoplasia

We have established the beginnings of a road map to understand how ventricular cells become specified, differentiate, and expand into a functional cardiac chamber (Fig. 5). The transcriptional networks described here provide clear evidence that disruption of pathways affecting ventricular growth could be the underlying etiology in a subset of children born with malformation of the right or left ventricle. As we learn details of the precise mechanisms through which the critical factors function, the challenge will lie in devising innovative methods to augment or modify the effects of gene mutations on ventricular development. Because most congenital heart disease likely occurs in a setting of heterozygous, predisposing mutations of one or more genes, modulation of activity of critical pathways in a preventive fashion may be useful in averting disease in genetically susceptible individuals.

Hemangioma of the oral cavity in a seven year old: a case report

A rare case of haemangioma of the oral cavity is presented. The lesion was treated using cryo-surgery.

Melanotic neuroectodermal tumour of infancy: a case report

Melanotic Neuroectodermal Tumour of Infancy is a rare tumour. Prompt recognition of such a case is essential for the Pediatric Dentist Presented here is a case of a four and a half month old child who reported in the dental out patient department of Guru Teg Bahadur Hospital with a swelling in the right anterior maxillary ridge region.

The combinatorial activities of Nkx2.5 and dHAND are essential for cardiac ventricle formation

Nkx2.5/Csx and dHAND/Hand2 are conserved transcription factors that are coexpressed in the precardiac mesoderm and early heart tube and control distinct developmental events during cardiogenesis. To understand whether Nkx2.5 and dHAND may function in overlapping genetic pathways, we generated mouse embryos lacking both Nkx2.5 and dHAND. Mice heterozygous for mutant alleles of Nkx2.5 and dHAND were viable. Although single Nkx2.5 or dHAND mutants have a morphological atrial and single ventricular chamber, Nkx2.5(-/-)dHAND(-/-) mutants had only a single cardiac chamber which was molecularly defined as the atrium. Complete ventricular dysgenesis was observed in Nkx2.5(-/-)dHAND(-/-) mutants; however, a precursor pool of ventricular cardiomyocytes was identified on the ventral surface of the heart tube. Because Nkx2.5 mutants failed to activate eHAND expression even in the early precardiac mesoderm, the Nkx2.5(-/-)dHAND(-/-) phenotype appears to reflect an effectively null state of dHAND and eHAND. Cell fate analysis in dHAND mutants suggests a role of HAND genes in survival and expansion of the ventricular segment, but not in specification of ventricular cardiomyocytes. Our molecular analyses also revealed the cooperative regulation of the homeodomain protein, Irx4, by Nkx2.5 and dHAND. These studies provide the first demonstration of gene mutations that result in ablation of the entire ventricular segment of the mammalian heart, and reveal essential transcriptional pathways for ventricular formation.