On the Equations and Boundary Conditions Governing Phonon-Mediated Heat Transfer in the Small Mean Free Path Limit: An Asymptotic Solution of the Boltzmann Equation

Using an asymptotic solution procedure, we construct solutions of the Boltzmann transport equation in the relaxation-time approximation in the limit of small Knudsen number, Kn << 1, to obtain continuum equations and boundary conditions governing phonon-mediated heat transfer in this limit. Our results show that, in the bulk, heat transfer is governed by the Fourier law of heat conduction, as expected. However, this description does not hold within distances on the order of a few mean free paths from the boundary; fortunately, this deviation from Fourier behavior can be captured by a universal boundary-layer solution of the Boltzmann equation that depends only on the material model and the phonon-boundary interaction model (Boltzmann boundary condition). Boundary conditions for the Fourier description follow from matching this inner solution to the outer (Fourier) solution. This procedure shows that the traditional no-jump boundary conditions are appropriate only to zeroth order in Kn. Solution to first order in Kn shows that the Fourier law needs to be complemented by jump boundary conditions with jump coefficients that depend on the material model and the phonon-boundary interaction model. In this work, we calculate these coefficients and the form of the jump conditions for an adiabatic-diffuse and a prescribed-temperature boundary in contact with a constant-relaxation-time material. Extension of this work to variable relaxation-time models is straightforward and will be discussed elsewhere. Our results are validated via comparisons with low-variance deviational Monte Carlo simulations

Adjoint-based deviational Monte Carlo methods for phonon transport calculations

In the field of linear transport, adjoint formulations exploit linearity to derive powerful reciprocity relations between a variety of quantities of interest. In this paper, we develop an adjoint formulation of the linearized Boltzmann transport equation for phonon transport. We use this formulation for accelerating deviational Monte Carlo simulations of complex, multiscale problems. Benefits include significant computational savings via direct variance reduction, or by enabling formulations which allow more efficient use of computational resources, such as formulations which provide high resolution in a particular phase-space dimension (e.g., spectral). We show that the proposed adjoint-based methods are particularly well suited to problems involving a wide range of length scales (e.g., nanometers to hundreds of microns) and lead to computational methods that can calculate quantities of interest with a cost that is independent of the system characteristic length scale, thus removing the traditional stiffness of kinetic descriptions. Applications to problems of current interest, such as simulation of transient thermoreflectance experiments or spectrally resolved calculation of the effective thermal conductivity of nanostructured materials, are presented and discussed in detail.United States. Dept. of Energy. Office of Science (Solid-State Solar-Thermal Energy Conversion Center Award DE-FG02-09ER46577)United States. Dept. of Energy. Office of Science (Solid-State Solar-Thermal Energy Conversion Center Award DE-SC0001299

Extending the range of validity of Fourier's law into the kinetic transport regime via asymptotic solution of the phonon Boltzmann transport equation

We derive the continuum equations and boundary conditions governing phonon-mediated heat transfer in the limit of a small but finite mean-free path from the asymptotic solution of the linearized Boltzmann equation in the relaxation time approximation. Our approach uses the ratio of the mean-free path to the characteristic system length scale, also known as the Knudsen number, as the expansion parameter to study the effects of boundaries on the breakdown of the Fourier description. We show that, in the bulk, the traditional heat conduction equation using Fourier's law as a constitutive relation is valid at least up to second order in the Knudsen number for steady problems and first order for time-dependent problems. However, this description does not hold within distances on the order of a few mean-free paths from the boundary; this breakdown is a result of kinetic effects that are always present in the boundary vicinity and require solution of a Boltzmann boundary layer problem to be determined. Matching the inner, boundary layer solution to the outer, bulk solution yields boundary conditions for the Fourier description as well as additive corrections in the form of universal kinetic boundary layers; both are found to be proportional to the bulk-solution gradients at the boundary and parametrized by the material model and the phonon-boundary interaction model (Boltzmann boundary condition). Our derivation shows that the traditional no-jump boundary condition for prescribed temperature boundaries and the no-flux boundary condition for diffusely reflecting boundaries are appropriate only to zeroth order in the Knudsen number; at higher order, boundary conditions are of the jump type. We illustrate the utility of the asymptotic solution procedure by demonstrating that it can be used to predict the Kapitza resistance (and temperature jump) associated with an interface between two materials. All results are validated via comparisons with low-variance deviational Monte Carlo simulations.United States. Dept. of Energy. Office of Science (Solid-State Solar-Thermal Energy Conversion Center Award DE-SC0001299)United States. Dept. of Energy. Office of Science (Solid-State Solar-Thermal Energy Conversion Center Award DE-FG02-09ER46577)Singapore-MIT Alliance for Research and Technolog

Deviational Phonons and Thermal Transport at the Nanoscale

We present a new method for simulating phonon transport at the nanoscale. The proposed approach is based on the recently developed energy-based deviational Monte Carlo method by the authors [Phys. Rev. B 84, 205331, 2011] which achieves significantly reduced statistical uncertainty compared to standard Monte Carlo methods by simulating only the deviation from equilibrium. Here, we show that under linearized conditions (small temperature differences) the trajectories of individual particles simulating the deviation from equilibrium can be decoupled and can thus be simulated independently, without introducing any additional approximation. This leads to a particularly simple and efficient simulation method that can be used to treat steady and transient phonon transport problems in arbitrary three-dimensional geometries.Singapore-MIT AllianceTotal-MIT Energy Initiative (Fellowship

Monte Carlo study of non-diffusive relaxation of a transient thermal grating in thin membranes

The impact of boundary scattering on non-diffusive thermal relaxation of a transient grating in thin membranes is rigorously analyzed using the multidimensional phononBoltzmann equation. The gray Boltzmann simulation results indicate that approximating models derived from previously reported one-dimensional relaxation model and Fuchs-Sondheimer model fail to describe the thermal relaxation of membranes with thickness comparable with phonon mean free path. Effective thermal conductivities from spectral Boltzmann simulations free of any fitting parameters are shown to agree reasonably well with experimental results. These findings are important for improving our fundamental understanding of non-diffusive thermal transport in membranes and other nanostructures.United States. Dept. of Energy. Office of Science (Solid-State Solar-Thermal Energy Conversion Center Award DE-SC0001299/DE-FG02-09ER46577

Isolation and characterization of a sponge-associated actinomycete that produces manzamines

Two Indonesian sponges, Acanthostrongylophora sp. Sponge 35 and Sponge 52, containing manzamine A were collected off the coast of Manado, Indonesia. Manzamines are a family of marine alkaloids that exhibit a complex molecular architecture and possess bioactivities including antitumour, antimicrobial, antiparasitic and insecticidal activities. Manzamines have been found in 17 different species of sponges with wide geographical distribution which has led to speculation that they may be produced by a microbial symbiont rather than by the sponges themselves. The sponges' microbial communities were investigated using 16S rRNA gene analysis and a rational culture-based microbiology approach in which specific bacterial groups were targeted. The molecular analysis of these microbial communities revealed that they were complex and diverse. Microbiological analyses were conducted on Acanthostrongylophora sp. with a particular emphasis on the isolation of actinomycetes because of the high number of actinomycete sequences in this sponge 16S rRNA gene clone library and their excellent track record as bioactive compound producers. One of the isolated actinomycetes, Micromonospora sp. strain M42, produces manzamine A and 8-hydroxy-manzamine, compounds initially detected in the sponge. A detailed analysis of Micromonospora sp. strain M42 showed that it grew on a wide range of salt concentrations with an optimal growth at 0-1% NaCl. Cultures of Micromonospora sp. strain M42 consistently produced manzamine A with a maximum yield of 1 mg/l. The genome size of Micromonospora sp. strain M42 was estimated at 6.7 Mb by pulsed field gel electrophoresis. The biosynthetic gene pathway encoding manzamine A was investigated using both biochemistry and molecular methods yet it remains elusive. Micromonospora sp. strain M42 underwent UV mutagenesis leading to isolation of mutants with yield of manzamine A improved by 3.5 fold. One of the mutants produces manzamine B, the putative biosynthetic precursor of manzamine A. A fosmid library of Micromonospora sp. strain M42 was constructed and low-pass genome sequencing gave insights into the strain's genome and revealed a high number of genes devoted to the production of secondary metabolites including polyketides and non-ribosomal peptides. The isolation of Micromonospora sp. strain M42 greatly improves the chances of manzamines becoming a drug class for treatment of malaria

Long-Term Isoflurane Therapy for Refractory Bronchospasm Associated with Herpes Simplex Pneumonia in a Heart Transplant Patient

A 47-year-old man with a history of heart transplant was admitted after severe traumatic brain injury and seizures. During mechanical ventilation, the patient developed bronchospasm that severely compromised respiratory function that led to cardiac arrest. After resuscitation, application of isoflurane through the Anaesthetic Conserving Device (AnaConDa) in the ICU successfully treated bronchospasm, provided adequate sedation, and enabled appropriate ventilation and diagnostic bronchoscopy. A subsequent bronchoalveolar lavage revealed a high amount of Herpes simplex DNA. Herpes simplex pneumonia was diagnosed and treated with acyclovir. Isoflurane treatment was applied for twelve days total without side effects on renal and cerebral function. The patient recovered quickly after the termination of sedation. At discharge, he was fully awake without focal neurological deficiency and his long-term outcome was excellent. This case demonstrates that isoflurane is a treatment option in life-threatening cases of bronchospasm and a safe option for long-term sedation

Ictal SPECT in Sturge-Weber syndrome

We report on a patient with right-sided Sturge-Weber syndrome (SWS), in whom earlier functional hemispherectomy failed. Subtraction of ictal and interictal single-photon-emission-computed-tomography (SPECT) superimposed on individual MRI showed a right fronto-orbital hyperperfusion, with a left-sided EEG seizure pattern. Ictal SPECT supported our assumption that right frontal originated seizure pattern propagated to left hemisphere via the remaining right frontal bridge. Right orbito-frontal resection and disconnection from corpus callosum resulted in seizure freedom

Whole-genome sequencing identifies genetic alterations in pediatric low-grade gliomas

The most common pediatric brain tumors are low-grade gliomas (LGGs). We used whole-genome sequencing to identify multiple new genetic alterations involving BRAF, RAF1, FGFR1, MYB, MYBL1 and genes with histone-related functions, including H3F3A and ATRX, in 39 LGGs and low-grade glioneuronal tumors (LGGNTs). Only a single non-silent somatic alteration was detected in 24 of 39 (62%) tumors. Intragenic duplications of the portion of FGFR1 encoding the tyrosine kinase domain (TKD) and rearrangements of MYB were recurrent and mutually exclusive in 53% of grade II diffuse LGGs. Transplantation of Trp53-null neonatal astrocytes expressing FGFR1 with the duplication involving the TKD into the brains of nude mice generated high-grade astrocytomas with short latency and 100% penetrance. FGFR1 with the duplication induced FGFR1 autophosphorylation and upregulation of the MAPK/ERK and PI3K pathways, which could be blocked by specific inhibitors. Focusing on the therapeutically challenging diffuse LGGs, our study of 151 tumors has discovered genetic alterations and potential therapeutic targets across the entire range of pediatric LGGs and LGGNTs.Jinghui Zhang, Gang Wu, Claudia P Miller, Ruth G Tatevossian, James D Dalton, Bo Tang, Wilda Orisme, Chandanamali Punchihewa, Matthew Parker, Ibrahim Qaddoumi, Fredrick A Boop, Charles Lu, Cyriac Kandoth, Li Ding, Ryan Lee, Robert Huether, Xiang Chen, Erin Hedlund, Panduka Nagahawatte, Michael Rusch, Kristy Boggs, Jinjun Cheng, Jared Becksfort, Jing Ma, Guangchun Song, Yongjin Li, Lei Wei, Jianmin Wang, Sheila Shurtleff, John Easton, David Zhao, Robert S Fulton, Lucinda L Fulton, David J Dooling, Bhavin Vadodaria, Heather L Mulder, Chunlao Tang, Kerri Ochoa, Charles G Mullighan, Amar Gajjar, Richard Kriwacki, Denise Sheer, Richard J Gilbertson, Elaine R Mardis, Richard K Wilson, James R Downing, Suzanne J Baker and David W Elliso

Factors associated with violence against women following the COVID-19 lockdown in France: Results from a prospective online survey

BACKGROUND: The aim of this research was to investigate the impact of the first COVID-19 lockdown (March 17th-May 11th 2020) on violence against women in France. METHODS: A prospective survey was conducted online between April 2th 2020 and July 5th 2020. Female respondents were recruited from social media networks using the snowball sampling method. Data were collected three times: during (2-19 April) and at the end (11-25 May) of the first lockdown, and following the first lockdown (20 June- 05 July). Sociodemographic variables, lockdown living conditions, financial impact of COVID, and history of psychiatric disorder were evaluated, together with changes in psychological distress over the lockdown period, and the risk of being assaulted post lockdown. RESULTS: Psychological distress was elevated and remained stable for most of the 1538 female respondents during lockdown. More than 7% of women were affected by physical or sexual violence post lockdown. Unwanted sexual contact accounted for the majority of abuse, but physical and sexual assault were also prevalent. The risk of being abused was higher for participants who had changed anxiety/insomnia symptoms over the lockdown period, and a history of abuse. DISCUSSION: Women who experienced changes in anxiety/insomnia symptoms during the COVID-19 lockdown were at higher risk than others of being assaulted post lockdown, especially when they were already socially vulnerable. While social and psychological factors accounting for these changes warrant further investigation, communication and preventive measures during pandemics should include initiatives tailored to women more vulnerable to violence