Graph 4-braid groups and Massey products

We first show that the braid group over a graph topologically containing no $\Theta$-shape subgraph has a presentation related only by commutators. Then using discrete Morse theory and triple Massey products, we prove that a graph topologically contains none of four prescribed graphs if and only if its 4-braid groups is a right-angled Artin group.Comment: 23 pages, 4 figure

Optical Generation and Detection of High-Frequency Focused Ultrasound and Associated Nonlinear Effects.

In this thesis, optical generation and detection of high-frequency ultrasound are presented. On the generation side, high-efficiency optical transmitters have been devised and developed which can generate high-frequency and high-amplitude pressure. Conventional optoacoustic transmitters have suffered from poor optoacoustic energy conversion efficiency (10-7~10-8). Therefore, pressure amplitudes were usually weak for long-range imaging (several cm) and too weak to induce any therapeutic effects. Here, far beyond such traditional regime, therapeutic pressure amplitudes of tens of MPa were achieved optoacoustically. First, high-efficiency optoacoustic sources were developed in planar geometries by using carbon nanotube-polymer composites. The planar transmitters could generate 18-fold stronger pressure than thin metallic films used as references, together with providing broadband and high-frequency spectra over 120 MHz. Then, the thin-film transmitters were formed on concave substrates to generate and simultaneously focus the ultrasound. Unprecedented optoacoustic pressure was achieved at lens focus: >50 MPa in positive and >20 MPa in negative peaks. These amplitudes were sufficient to induce strong shock waves and acoustic cavitation. Due to the high-frequency operation, such therapeutic pressure and the induced effects were tightly localized onto focal widths of 75 um in lateral and 400 um in axial directions, which are an order of magnitude smaller than those of traditional piezoelectric transducers. The shock waves and the cavitation effects were investigated in various ways. High focal gains and short distances for shock formation were suggested as main features. The optoacoustic approach is expected to open numerous opportunities for a broad range of biomedical applications demanding high-accuracy treatment with minimal damage volumes around focal zones. For optical detection of ultrasound, optical microring resonators have been used due to their broadband frequency responses (~100 MHz) and high sensitivity. However, their spatial responses due to the particular ring shape have not been investigated especially for high-frequency ranges. Here, the microring responses were characterized in this regime. As a final subject, the microrings were used to detect focused ultrasound and realize novel optoacoustic 4f imaging systems which have capabilities of fast 3-D imaging without requiring mathematical reconstruction steps. High-resolution performances were demonstrated by resolving polymer microspheres of 100-um diameter.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91573/1/hwbaac_1.pd

Role of dermal melanocytes in cutaneous pigmentation of stasis dermatitis: a histopathological study of 20 cases.

Stasis dermatitis is an itchy, scaly, and hyperpigmented condition of the lower leg due to venous insufficiency. Hemosiderin and/or melanin have been considered responsible for the brown pigmentation. However, there are not sufficient histopathologic studies. In this retrospective study the hospital records and biopsy slides of 20 patients were reviewed to determine the pathogenetic mechanisms of brown pigmentation in stasis dermatitis. Fifteen were men (75%) and 5 were women (25%) with a mean age of 46.2+/-8.2 yr (18-76), mean age at onset of 43.4+/-18.0 yr (17-73), and a mean duration of the disease 2.8+/-2.5 yr (0.25-10). All patients had varicose vein and complained of pruritus. On histopathologic evaluation, two cases out of 20 (3 skin biopsy specimens from 25 samples) showed dermal melanocytes containing melanin, and incontinence of melanin pigment was observed in 5 cases, which indicates that melanin pigments from epidermis could contribute to cutaneous pigmentation in stasis dermatitis. However, the existence of dermal melanocytes in two cases cannot be explained because normally the dermis contains no melanocytes. Further studies concerning the role of iron or inflammatory cytokines on the development of dermal melanocytes should be conducted

CPEM: Accurate cancer type classification based on somatic alterations using an ensemble of a random forest and a deep neural network

With recent advances in DNA sequencing technologies, fast acquisition of large-scale genomic data has become commonplace. For cancer studies, in particular, there is an increasing need for the classification of cancer type based on somatic alterations detected from sequencing analyses. However, the ever-increasing size and complexity of the data make the classification task extremely challenging. In this study, we evaluate the contributions of various input features, such as mutation profiles, mutation rates, mutation spectra and signatures, and somatic copy number alterations that can be derived from genomic data, and further utilize them for accurate cancer type classification. We introduce a novel ensemble of machine learning classifiers, called CPEM (Cancer Predictor using an Ensemble Model), which is tested on 7,002 samples representing over 31 different cancer types collected from The Cancer Genome Atlas (TCGA) database. We first systematically examined the impact of the input features. Features known to be associated with specific cancers had relatively high importance in our initial prediction model. We further investigated various machine learning classifiers and feature selection methods to derive the ensemble-based cancer type prediction model achieving up to 84% classification accuracy in the nested 10-fold cross-validation. Finally, we narrowed down the target cancers to the six most common types and achieved up to 94% accuracy

Efficient Photoacoustic Conversion in Optical Nanomaterials and Composites

Photoacoustic pulses generated by pulsed laser irradiation have the characteristics of high frequency and wide bandwidth, which are desirable for imaging and sensing. Efficient photoacoustic composites have been developed for fabricating photoacoustic transmitters capable of generating high‐amplitude ultrasound. Here, recent advances in photoacoustic transmitters are reviewed from an application perspective, starting with the fundamental aspects of photoacoustic generation. The topics discussed include various composite materials for photoacoustic generation, and their applications such as high‐amplitude therapy, imaging and sensing, and photoacoustic waveform control.Photoacoustic transmitters using pulsed laser irradiation onto optical nanomaterials have been developed for generating strong photoacoustic pulses, enabling interesting applications. Recent advances in photoacoustic transmitters are reviewed from an application perspective, starting with the fundamental aspects of photoacoustic generation.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147165/1/adom201800491_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147165/2/adom201800491.pd

Low density carbon nanotube forest as an index-matched and near perfect absorption coating

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98687/1/ApplPhysLett_99_211103.pd