Fragmentation of star-forming filaments in the X-shape Nebula of the California molecular cloud

Dense molecular filaments are central to the star formation process, but the detailed manner in which they fragment into prestellar cores is not yet well understood. Here, we investigate the fragmentation properties and dynamical state of several star-forming filaments in the X-shape Nebula region of the California MC, in an effort to shed some light on this issue. We used multi-wavelength far-infrared images from Herschel and the getsources and getfilaments extraction methods to identify dense cores and filaments and derive their basic properties. We also used a map of $\rm ^{13}CO (2-1)$ emission from SMT 10m submillimeter telescope to constrain the dynamical state of the filaments. We identified 10 filaments, as well as 57 dense cores. Two star-forming filaments (# 8 and # 10) stand out in that they harbor quasi-periodic chains of dense cores with a typical projected core spacing of $\sim$0.15 pc. These two filaments have thermally supercritical line masses and are not static. Filament~8 exhibits a prominent transverse velocity gradient, suggesting that it is accreting gas from the parent cloud gas reservoir. In both cases, the observed (projected) core spacing is similar to the filament width and significantly shorter than the canonical separation of $\sim \,$4 times the filament width predicted by classical cylinder fragmentation theory. We suggest that continuous accretion of gas onto the two star-forming filaments, as well as geometrical bending of the filaments, may account for the observed core spacing. Our findings suggest that the characteristic fragmentation lengthscale of molecular filaments is quite sensitive to external perturbations from the parent cloud, such as gravitational accretion of ambient material.Comment: 14 pages, 12 figures, accepted for publication in A&

Etching kinetics and surface roughening of polysilicon and dielectric materials in inductively coupled plasma beams

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2007.Includes bibliographical references.Plasma etching processes often roughen the feature sidewalls forming anisotropic striations. A clear understanding of the origin and control of sidewall roughening is extremely desirable, particularly at the gate level where variations in line width can adversely impact the electrical performance of the device. In addition, at the back end, feature sidewall roughness of the dielectric materials might degrade the resolution of contacts, interfere with the deposition of conformal liner materials, and make the process integration challengeable. In an inductively coupled plasma apparatus, the etching behavior on real feature sidewalls was simulated by etching blank films at grazing ion bombardment angles. The angular etching yields of polysilicon and dielectric materials in Ar, C12/Ar, and C4F8/Ar plasma beams were studied as a function of ion bombardment energy, ion bombardment angle, etching time, plasma pressure, and plasma composition. Interestingly, the effective neutral-to-ion flux ratio was the primary factor influencing the etching yield. A typical sputtering angular yield curve, with a peak around 600 off-normal angle, was formed at non-saturated etching regime, while an ion-enhanced-etching angular yield curve peaked around 650 was observed in the saturated etching regime.(cont.) In Ar plasma, various films remained smooth after etching at normal angle but became rougher at grazing angles. Specifically, the striation structure formed at grazing angles could be either parallel or transverse to the beam impingement direction. Encouragingly, the sputtering caused roughening at different off-normal angles could be qualitatively explained by the corresponding angular dependent etching yield curve. In fluorocarbon plasmas, the roughening of thermal silicon dioxide and low-k coral films at grazing ion bombardment angles depended on both the etching kinetics and the etching chemistry. In particular, the surface roughened when the etching process was physical-sputtering like (at low neutral-to-ion flux ratios), even though the polymer deposition effect was trivial; when the etching kinetics was dominated by ion-enhanced etching (at high neutral-to-ion flux ratios), the roughening was mainly caused by the local polymer deposition effects. Moreover, surfaces could be etched without roughening at intermediate neutral-to-ion flux ratios and/or with the addition of oxygen to the discharge. The oxygen addition broadened the region over which etching without roughening can be performed.(cont.) Additionally, the local-polymer-deposition effect can be used to explain the surface roughening of porous low-k films in fluorocarbon plasmas. Last, it was shown that RMS roughness is not adequate to represent the surface roughness on etched surfaces, especially when anisotropic striations exist. Instead, statistical methods such as the power spectral density and geostatistical analysis are capable of measuring the surface roughening in both vertical and lateral dimensions. In this way, the spatial variation of the streaks formed during plasma etching can be characterized quantitatively.by Yunpeng Yin.Ph.D

Toward an intelligent multimodal interface for natural interaction

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 73-76).Advances in technology are enabling novel approaches to human-computer interaction (HCI) in a wide variety of devices and settings (e.g., the Microsoft® Surface, the Nintendo® Wii, iPhone®, etc.). While many of these devices have been commercially successful, the use of multimodal interaction technology is still not well understood from a more principled system design or cognitive science perspective. The long-term goal of our research is to build an intelligent multimodal interface for natural interaction that can serve as a testbed for enabling the formulation of a more principled system design framework for multimodal HCI. This thesis focuses on the gesture input modality. Using a new hand tracking technology capable of tracking 3D hand postures in real-time, we developed a recognition system for continuous natural gestures. By nature gestures, we mean the ones encountered in spontaneous interaction, rather than a set of artificial gestures designed for the convenience of recognition. To date we have achieved 96% accuracy on isolated gesture recognition, and 74% correct rate on continuous gesture recognition with data from different users and twelve gesture classes. We are able to connect the gesture recognition system with Google Earth, enabling gestural control of a 3D map. In particular, users can do 3D tilting of the map using non touch-based gesture which is more intuitive than touch-based ones. We also did an exploratory user study to observe natural behavior under a urban search and rescue scenario with a large tabletop display. The qualitative results from the study provides us with good starting points for understanding how users naturally gesture, and how to integrate different modalities. This thesis has set the stage for further development towards our long-term goal.by Ying Yin.S.M

Tumor-penetrating delivery of small interfering RNA therapeutics

Thesis (Ph. D. in Medical Engineering)--Harvard-MIT Program in Health Sciences and Technology, 2012.Vita. Cataloged from PDF version of thesis.Includes bibliographical references (p. 234-250).Efforts to sequence cancer genomes have begun to uncover comprehensive lists of genes altered in cancer. Unfortunately, the number and complexity of identified alterations has made dissecting the underlying biology of cancer difficult, as many genes are not amenable to manipulation by small molecules or antibodies. RNA interference (RNAi) provides a direct way to assess and act on putative cancer targets. However, the translation of RNAi into the clinic has been thwarted by the "delivery" challenge, as small interfering RNA (siRNA) therapeutics must overcome clearance mechanisms and penetrate into tumor tissues to access cancer cells. This thesis sought to develop nanotechnology-based platforms to rapidly discover and validate cancer targets in vivo. First, we developed versatile surface chemistries for nanoparticle tumor targeting. Leveraging new discoveries in amplified transvascular transport, we designed a siRNA delivery system that integrates the tumor specificity and tissue-penetrating ability of tumor-penetrating peptides with membrane penetration properties of protein transduction domains to direct siRNA to tumors in vivo. Second, we utilized this delivery system to bridge the gap between cancer genomic discovery and in vivo target validation. Comprehensive analysis of ovarian cancer genomes identified candidate targets that are undruggable by traditional approaches. Tumor-penetrating delivery of siRNA against these genes potently impeded the growth of ovarian tumors in mice and improved survival, thereby credentialing their roles in tumor initiation and maintenance. Lastly, we described efforts extending this platform for clinical translation. Mechanistic studies identified functional properties that favored receptor-specific siRNA delivery. We also explored a strategy to improve the microdistribution of successively dosed siRNA therapeutics through modulating the tumor microenvironment. Finally, we investigated the utility of the system in primary human tumors derived from patients with ovarian cancer. Together, these findings illustrate that the combination of cancer genomics with the engineering of siRNA delivery nanomaterials establishes a platform for discovering genes amenable to RNAi therapies. As efforts in genome sequencing accelerate, this platform illustrates a path to clinical translation in humans.by Yin Ren.Ph.D.in Medical Engineerin

Ultrathin 2 nm gold as ideal impedance-matched absorber for infrared light

Thermal detectors are a cornerstone of infrared (IR) and terahertz (THz) technology due to their broad spectral range. These detectors call for suitable broad spectral absorbers with minimalthermal mass. Often this is realized by plasmonic absorbers, which ensure a high absorptivity butonly for a narrow spectral band. Alternativly, a common approach is based on impedance-matching the sheet resistance of a thin metallic film to half the free-space impedance. Thereby, it is possible to achieve a wavelength-independent absorptivity of up to 50 %, depending on the dielectric properties of the underlying substrate. However, existing absorber films typicallyrequire a thickness of the order of tens of nanometers, such as titanium nitride (14 nm), whichcan significantly deteriorate the response of a thermal transducers. Here, we present the application of ultrathin gold (2 nm) on top of a 1.2 nm copper oxide seed layer as an effective IR absorber. An almost wavelength-independent and long-time stable absorptivity of 47(3) %, ranging from 2 $\mu$m to 20 $\mu$m, could be obtained and is further discussed. The presented gold thin-film represents analmost ideal impedance-matched IR absorber that allows a significant improvement of state-of-the-art thermal detector technology

Proximity of Iron Pnictide Superconductors to a Quantum Tricritical Point

We determine the nature of the magnetic quantum critical point in the doped LaFeAsO using a set of constrained density functional calculations that provide ab initio coefficients for a Landau order parameter analysis. The system turns out to be remarkably close to a quantum tricritical point, where the nature of the phase transition changes from first to second order. We compare with the effective field theory and discuss the experimental consequences.Comment: 4 pages, 4 figure

Machine-Part cell formation through visual decipherable clustering of Self Organizing Map

Machine-part cell formation is used in cellular manufacturing in order to process a large variety, quality, lower work in process levels, reducing manufacturing lead-time and customer response time while retaining flexibility for new products. This paper presents a new and novel approach for obtaining machine cells and part families. In the cellular manufacturing the fundamental problem is the formation of part families and machine cells. The present paper deals with the Self Organising Map (SOM) method an unsupervised learning algorithm in Artificial Intelligence, and has been used as a visually decipherable clustering tool of machine-part cell formation. The objective of the paper is to cluster the binary machine-part matrix through visually decipherable cluster of SOM color-coding and labelling via the SOM map nodes in such a way that the part families are processed in that machine cells. The Umatrix, component plane, principal component projection, scatter plot and histogram of SOM have been reported in the present work for the successful visualization of the machine-part cell formation. Computational result with the proposed algorithm on a set of group technology problems available in the literature is also presented. The proposed SOM approach produced solutions with a grouping efficacy that is at least as good as any results earlier reported in the literature and improved the grouping efficacy for 70% of the problems and found immensely useful to both industry practitioners and researchers.Comment: 18 pages,3 table, 4 figure

Strong coupling, discrete symmetry and flavour

We show how two principles - strong coupling and discrete symmetry - can work together to generate the flavour structure of the Standard Model. We propose that in the UV the full theory has a discrete flavour symmetry, typically only associated with tribimaximal mixing in the neutrino sector. Hierarchies in the particle masses and mixing matrices then emerge from multiple strongly coupled sectors that break this symmetry. This allows for a realistic flavour structure, even in models built around an underlying grand unified theory. We use two different techniques to understand the strongly coupled physics: confinement in N=1 supersymmetry and the AdS/CFT correspondence. Both approaches yield equivalent results and can be represented in a clear, graphical way where the flavour symmetry is realised geometrically.Comment: 31 pages, 5 figures, updated references and figure

Phonons and related properties of extended systems from density-functional perturbation theory

This article reviews the current status of lattice-dynamical calculations in crystals, using density-functional perturbation theory, with emphasis on the plane-wave pseudo-potential method. Several specialized topics are treated, including the implementation for metals, the calculation of the response to macroscopic electric fields and their relevance to long wave-length vibrations in polar materials, the response to strain deformations, and higher-order responses. The success of this methodology is demonstrated with a number of applications existing in the literature.Comment: 52 pages, 14 figures, submitted to Review of Modern Physic