Experimental study on Compton camera for boron neutron capture therapy applications.

Boron neutron capture therapy (BNCT) is a high-dose-intensive radiation therapy that has gained popularity due to advancements in accelerator neutron sources. To determine the dose for BNCT, it is necessary to know the difficult-to-determine boron concentration and neutron fluence. To estimate this dose, we propose a method of measuring the prompt γ-rays (PGs) from the boron neutron capture reaction (BNCR) using a Compton camera. We performed a fundamental experiment to verify basic imaging performance and the ability to discern the PGs from 511 keV annihilation γ-rays. A Si/CdTe Compton camera was used to image the BNCR and showed an energy peak of 478 keV PGs, separate from the annihilation γ-ray peak. The Compton camera could visualize the boron target with low neutron intensity and high boron concentration. This study experimentally confirms the ability of Si/CdTe Compton cameras to image BNCRs.

Experimental binding energies for the metal complexes [Mg(NH3)n]2+, [Ca(NH3)n]2+, and [Sr(NH3)n]2+ for n = 4-20 determined from kinetic energy release measurements.

A supersonic source of clusters has been used to prepare neutral complexes of ammonia in association with a metal atom. From these complexes the following metal-containing dications have been generated: [Mg(NH3)n](2+), [Ca(NH3)n](2+), and [Sr(NH3)n](2+), and for n in the range 4-20, kinetic energy release measurements following the evaporation of a single molecule have been undertaken using a high resolution mass spectrometer. Using finite heat bath theory, these data have been transformed into binding energies for individual ammonia molecules attached to each of the three cluster systems. In the larger complexes (n > 6) the results exhibit a consistent trend, whereby the experimental binding energy data for all three metal ions are very similar, suggesting that the magnitude of the charge rather than charge density influences the strength of the interaction. From a comparison with data recorded previously for (NH3)nH(+) it is found that the 2+ charge on a metal ion has an effect on the binding energy of molecules in complexes containing up to 20 solvent molecules. Although subject to comparatively large experimental errors, the results recorded for Ca(2+) and Sr(2+) when n ≤ 6 show evidence for the formation of an inner solvation shell containing up to 6 molecules. However, Mg(2+) exhibits relatively low binding energies when n = 5 and 6, which suggests that a second shell starts to form before there are 6 ammonia molecules bound to the metal ion. This conclusion is supported by DFT calculations and it is proposed that these complexes could take the form [Mg(NH3)4(NH3)](2+) when n = 5 and either [Mg(NH3)4(NH3)2](2+) or [Mg(NH3)5(NH3)](2+) when n = 6. In each case, additional molecules are hydrogen bonded to one or more molecules in the inner solvation shell.

Prevalence and risk factors of soil-transmitted helminth infection in Nepal.

BACKGROUND: The purpose of this study is to evaluate the prevalence and intensity and examine the risk factors of soil transmitted helminth (STH; i.e., roundworm [Ascaris lumbricoides], hookworms [Ancylostoma duodenale and Necator americanus], and whipworm [Trichuris trichiura]) infections in Nepal. METHODS: Five hundred and ninety-four adults (256 men and 338 women) were selected via convenience sampling from five communities in Nepal. The Kato-Katz method was used to assess the prevalence and intensity of STH infection in this population. RESULTS: Prevalence of STH infection ranged from 3.3% in Birendranagar in Chitwan, 3.5% in Kuleshor in Kathmandu, 11.7% in Kanyam in Ilam, 17.0% in Dhikurpokhari in Kaski and 51.4% in Khokana in Lalitpur District [corrected]. Multivariable regression analysis revealed that not using soap for hand-washing was significantly associated with the prevalence and infection intensity of roundworm, hookworms and whipworm. Similarly, not wearing sandals or shoes outside was significantly associated with the prevalence and infection intensity of roundworm and hookworms, but not with infection intensity of whipworm. Literacy, being underweight or overweight, anemia and occupation were not associated with prevalence and intensity of roundworm and hookworms infection, but there was an association between occupation and the prevalence of whipworm infection. CONCLUSION: STH infection was associated with individual hygiene behavior, but not with nutritional status or socio-demographic characteristics. Health policy focusing on changing individual hygiene behaviors might be useful in addressing STH infection in Nepal.

Alpine cushion plants inhibit the loss of phylogenetic diversity in severe environments.

Biotic interactions can shape phylogenetic community structure (PCS). However, we do not know how the asymmetric effects of foundation species on communities extend to effects on PCS. We assessed PCS of alpine plant communities around the world, both within cushion plant foundation species and adjacent open ground, and compared the effects of foundation species and climate on alpha (within-microsite), beta (between open and cushion) and gamma (open and cushion combined) PCS. In the open, alpha PCS shifted from highly related to distantly related with increasing potential productivity. However, we found no relationship between gamma PCS and climate, due to divergence in phylogenetic composition between cushion and open sub-communities in severe environments, as demonstrated by increasing phylo-beta diversity. Thus, foundation species functioned as micro-refugia by facilitating less stress-tolerant lineages in severe environments, erasing a global productivity - phylogenetic diversity relationship that would go undetected without accounting for this important biotic interaction.

Multi-photon ionization and fragmentation of uracil: neutral excited-state ring opening and hydration effects.

Multi-photon ionization (MPI) of the RNA base uracil has been studied in the wavelength range 220-270 nm, coinciding with excitation to the S2(ππ*) state. A fragment ion at m/z = 84 was produced by 2-photon absorption at wavelengths ≤232 nm and assigned to C3H4N2O(+) following CO abstraction. This ion has not been observed in alternative dissociative ionization processes (notably electron impact) and its threshold is close to recent calculations of the minimum activation energy for a ring opening conical intersection to a σ(n-π)π* closed shell state. Moreover, the predicted ring opening transition leaves a CO group at one end of the isomer, apparently vulnerable to abstraction. An MPI mass spectrum of uracil-water clusters is presented for the first time and compared with an equivalent dry measurement. Hydration enhances certain fragment ion pathways (particularly C3H3NO(+)) but represses C3H4N2O(+) production. This indicates that hydrogen bonding to water stabilizes uracil with respect to neutral excited-state ring opening.

Health status of married women residing five communities in Nepal: unexpectedly high prevalence of anemia in a well-off community of Kathmandu.

The high prevalence of anemia and underweight among reproductive age women is a serious health concern in Nepal. The objective of the present study was to describe anemia prevalence and nutritional status of married women in Nepal. Total of 278 women were included in the present analysis. The five communities included an urban commercial area (W) in Kathmandu, an agricultural village (K) in Lalitpur District, an agricultural village in Chitwan District (C) and one in Ilam District (I) with intensive cash cropping, and another rural village in Kaski District (P) with high number of international out-migration of males. The study procedure included anthropometric measurements, blood collection for hemoglobin measurement, and stool collection for examination of hookworm infection, and a structured interview on their reproductive history including contraceptive use. The altitude adjusted prevalence of anemia was 65%, 23%, 16%, 49% and 58% in communities C, I, K, P and W respectively. The hookworm prevalence of each community was not associated with the anemia prevalence. In the urban well-off community W, although 38% of the women had BMI > or = 25 and only 2% of women had BMI<18.5, 58% of the women were anemic. A logistic regression analysis on the anemia risk at the individual level showed no effect of helminth infection, but a significant negative effect of Depo-Provera (depot-medroxyprogesterone acetate) use. Causes of high anemia prevalence among the women resided in the urban well-off area should be investigated in future studies.

Increasing access to safe abortion services through auxiliary nurse midwives trained as skilled birth attendants.

BACKGROUND: The use of medical abortion methods was approved by Department of Health Services in 2009 and introduced in hospitals and a few primary health centres (PHCs). Access would increase if services were available at health post level and provided by auxiliary nurse midwives trained as skilled birth attendants. Evidence from South Africa, Bangladesh, Nepal and Vietnam show that mid-level health workers can provide medical abortion safely. OBJECTIVES: To determine the best way to implement the new strategies of medical abortion into the existing health system of Nepal; and to facilitate its full-scale implementation, monitoring and evaluation. METHODS: An implementation research involving a baseline study, implementation phase and end line study was done in ten districts covering five development regions from July 2010 to June 2011. Both qualitative and quantitative methods were used. RESULTS: Of 1,799 medical abortion clients who received service, 46% were disadvantaged Janjati, 14% were Dalit, 42% were upper caste groups and rest were advantaged Janjati (7%), Muslim (1%) and others. 14% were referred by female community health volunteers and 56% were referred by others. Complication rate of 0.3% was well below acceptable levels. Condom use increased from 8% to 28% by the end of study. Use of Pills, Depo, intra uterine devices and implants also increased, but use of long acting family planning methods was negligible. CONCLUSIONS: This model should be replicated nationwide at health posts and sub-health posts where auxiliary nurse midwives are available 24 hours/day. Focus should be given first to those areas where access is difficult, time consuming and costly.

Mechanisms and dynamics of the metastable decay in Ar2+.

A detailed experimental as well as theoretical investigation of the properties of the metastable dissociation Ar2+ --> Ar+ + Ar is presented. The mass-analyzed ion kinetic energy (MIKE) scan technique has been performed using a three sector field mass spectrometer. The possible mechanisms of the metastability of Ar2+ have been examined and the observed decay process is assigned to the II(1/2)(u)-->I(1/2)(g) bound to continuum radiative transition, in agreement with earlier work. The calculation of the theoretical shape of the kinetic energy release distribution of fragment ions allowed us to construct the theoretical MIKE peak and compare it with the raw experimental data. The accuracy of various sets of potential energy curves for Ar2+ is discussed, as well as the way of production of the metastable Ar2+[II(1/2)(u)] electronic state by electron impact. Excellent agreement between the experimental data and theoretical model has been observed.

Probing electronic states of Ne2+ and Ar2+ by measuring kinetic-energy-release distributions.

Dissociative decay of metastable, electronically excited neon and argon dimer ions produces fragment ions with strikingly dissimilar kinetic-energy-release distributions. The distributions have been modeled based on ab initio calculations of potential energy curves. The unusual bimodal distribution observed for dissociation of Ne2+ arises from competition between radiative and nonradiative decay of the long-lived II(1/2)(u) state. For Ar2+, however, electronic predissociation is insignificant.