Geodesics in Heat

We introduce the heat method for computing the shortest geodesic distance to a specified subset (e.g., point or curve) of a given domain. The heat method is robust, efficient, and simple to implement since it is based on solving a pair of standard linear elliptic problems. The method represents a significant breakthrough in the practical computation of distance on a wide variety of geometric domains, since the resulting linear systems can be prefactored once and subsequently solved in near-linear time. In practice, distance can be updated via the heat method an order of magnitude faster than with state-of-the-art methods while maintaining a comparable level of accuracy. We provide numerical evidence that the method converges to the exact geodesic distance in the limit of refinement; we also explore smoothed approximations of distance suitable for applications where more regularity is required

Application of photosynthetic N2-fixing cyanobacteria to the CELSS program

Commercially available air lift fermentors were used to simultaneously monitor biomass production, N2-fixation, photosynthesis, respiration, and sensitivity to oxidative damage during growth under various nutritional and light regimes, to establish a data base for the integration of these organisms into a Closed Ecological Life Support System (CELSS) program. Certain cyanobacterial species have the unique ability to reduce atmospheric N2 to organic nitrogen. These organisms combine the ease of cultivation characteristics of prokaryotes with the fully developed photosynthetic apparatus of higher plants. This, along with their ability to adapt to changes in their environment by modulation of certain biochemical pathways, make them attractive candidates for incorporation into the CELSS program

A comparison of the Bekesy-type test with Roger's monaural test of Fowler's binaural test for recruitment

Thesis (Ed.M.)--Boston Universit

Fourier PCA and Robust Tensor Decomposition

Fourier PCA is Principal Component Analysis of a matrix obtained from higher order derivatives of the logarithm of the Fourier transform of a distribution.We make this method algorithmic by developing a tensor decomposition method for a pair of tensors sharing the same vectors in rank-$1$ decompositions. Our main application is the first provably polynomial-time algorithm for underdetermined ICA, i.e., learning an $n \times m$ matrix $A$ from observations $y=Ax$ where $x$ is drawn from an unknown product distribution with arbitrary non-Gaussian components. The number of component distributions $m$ can be arbitrarily higher than the dimension $n$ and the columns of $A$ only need to satisfy a natural and efficiently verifiable nondegeneracy condition. As a second application, we give an alternative algorithm for learning mixtures of spherical Gaussians with linearly independent means. These results also hold in the presence of Gaussian noise.Comment: Extensively revised; details added; minor errors corrected; exposition improve

Long Wavelength VCSELs and VCSEL-Based Processing of Microwave Signals

We address the challenge of decreasing the size, cost and power consumption for practical applications of next generation microwave photonics systems by using long-wavelength vertical cavity surface emitting lasers. Several demonstrations of new concepts of microwave photonics devices are presented and discussed

Oxidative Stress Detection With Escherichia Coli Harboring A katG\u27::lux Fusion

A plasmid containing a transcriptional fusion of the Escherichia coli katG promoter to a truncated Vibrio fischeri lux operon (luxCDABE) was constructed. An E. coli strain bearing this plasmid (strain DPD2511) exhibited low basal levels of luminescence, which increased up to 1,000-fold in the presence of hydrogen peroxide, organic peroxides, redox-cycling agents (methyl viologen and menadione), a hydrogen peroxide-producing enzyme system (xanthine and xanthine oxidase), and cigarette smoke. An oxyR deletion abolished hydrogen peroxide-dependent induction, confirming that oxyR controlled katG\u27::lux luminescence. Light emission was also induced by ethanol by an unexplained mechanism. A marked synergistic response was observed when cells were exposed to both ethanol and hydrogen peroxide; the level of luminescence measured in the presence of both inducers was much higher than the sum of the level of luminescence observed with ethanol and the level of luminescence observed with hydrogen peroxide. It is suggested that this construction or similar constructions may be used as a tool for assaying oxidant and antioxidant properties of chemicals, as a biosensor for environmental monitoring and as a tool for studying cellular responses to oxidative hazards

Detection Of DNA Damage By Use Of Escherichia Coli Carrying recA\u27::lux, uvrA\u27::lux, And alkA\u27::lux Reporter Plasmids

Plasmids were constructed in which DNA damage-inducible promoters recA, uvrA, and alkA from Escherichia coli were fused to the Vibrio fischeri luxCDABE operon. Introduction of these plasmids into E. coli allowed the detection of a dose-dependent response to DNA-damaging agents, such as mitomycin and UV irradiation. Bioluminescence was measured in real time over extended periods. The fusion of the recA promoter to luxCDABE showed the most dramatic and sensitive responses. lexA dependence of the bioluminescent SOS response was demonstrated, confirming that this biosensor\u27s reports were transmitted by the expected regulatory circuitry. Comparisons were made between luxCDABE and lacZ fusions to each promoter. It is suggested that the lux biosensors may have use in monitoring chemical, physical, and genotoxic agents as well as in further characterizing the mechanisms of DNA repair

Chevkinite-Group Minerals from Granulite-Facies Metamorphic Rocks and Associated Pegmatites of East Antarctica and South India

Electron microprobe data are presented for chevkinite-group minerals from granulite-facies rocks and associated pegmatities of the Napier Complex and Mawson Station charnockite in East Antarctica and from the Eastern Ghats, South India. Their compositions conform to the general formula for this group, viz. A(4)BC(2)D(2)Si(4)O(22) where, in the analysed specimens A = (rare-earth elements (REE), Ca, Y, Th), B = Fe(2+) Mg, C = (Al, Mg, Ti, Fe(2+), Fe(3+), Zr) and D = Ti and plot within the perrierite field oftlic total Fe (as FeO) (wt.%) vs. CaO (wt.%) discriminator diagram of Macdonald and Belkin (2002). In contrast to most chevkinite-group minerals, the A site shows unusual enrichment in the MREE and HREE relative to the LREE and Ca. In one sample from the Napier Complex, Y is the dominant cation among the total REE + Y in the A site, the first reported case of Y-dominance in the chevkinite group. The minerals include the most Al-rich yet reported in the chevkinite group (\u3c= 9.15 wt.% Al(2)O(3)), sufficient to fill the C site in two samples. Conversely, the amount of Ti in these samples does not fill the D site. and, thus, some of the Al could be making up the deficiency at D, a situation not previously reported in the chevkinite group. Fe abudances are low, requiring Mg to occupy up to 45% of the B site. The chevkinite-group minerals analysed originated from three distinct parageneses: (1) pegmatites containing hornblende and orthopyroxene or garnet; (2) orthopyroxene-bearing gneiss and granulite; (3) highly aluminous paragneisses in which the associated minerals are relatively magnesian or aluminous. Chevkinite-group minerals from the first two parageneses have relatively high FeO content and low MgO and Al(2)O(3) contents; their compositions plot in the field for mafic and intermediate igneous rocks. In contrast, chevkinite-group minerals from the third paragenesis are notably more aluminous and have greater Mg/Fe ratios

Sea Changes Ashore : The Ocean and Iceland's Herring Captial

The story of Siglufjörður (Siglufjordur), a north Iceland village that became the "Herring Capital of the World," provides a case study of complex interactions between physical, biological, and social systems. Siglufjörður's natural capital - a good harbor and proximity to prime herring grounds - contributed to its development as a major fishing center during the first half of the 20th century. This herring fishery was initiated by Norwegians, but subsequently expanded by Icelanders to such an extent that the fishery, and Siglufjörður in particular, became engines helping to pull the whole Icelandic economy. During the golden years of this "herring adventure," Siglufjörður opened unprecedented economic and social opportunities. Unfortunately, the fishing boom reflected unsustainably high catch rates. In the years following World War II, overfishing by an international fleet eroded the once-huge herring stock. Then, in the mid-1960s, large-scale physical changes took place in the seas north of Iceland. These physical changes had ecological consequences that led to the loss of the herring's main food supply. Severe environmental stress, combined with heavy fishing pressure, drove the herring stocks toward collapse. Siglufjörður found itself first marginalized, then shut out as the herring progressively vanished. During the decades following the 1968 collapse, this former boomtown has sought alternatives for sustainable development.L'histoire de Siglufjörður (Siglufjordur), un village du nord de l'Islande qui acquit le statut de «Capitale mondiale du hareng», offre une étude de cas des interactions complexes qui ont lieu entre des systèmes physiques, biologiques et sociaux. Le capital naturel de Siglufjörður - un bon port et la proximité de bancs de harengs exceptionnels - a contribué à sa mise en valeur comme grand centre de pêche durant la première moitié du XXe siècle. La pêche au hareng, pratiquée tout d'abord par les Norvégiens, prit un tel essor avec les Islandais qu'elle devint, avec Siglufjörður en particulier, le moteur qui contribua à faire marcher toute l'économie de l'Islande. Durant les années fastes de cette «ère du hareng», il y eut à Siglufjörður des ouvertures économiques et sociales sans précédent. Malheureusement, le boom de la pêche représentait des taux de prises trop élevés pour être durables. Au cours des années qui suivirent la Deuxième Guerre mondiale, la surpêche pratiquée par une flottille internationale fit baisser le stock de harengs jadis abondant. Puis au milieu des années 1960, il se produisit, dans les eaux situées au nord de l'Islande, des changements à grande échelle sur le plan physique. Ces derniers eurent des conséquences écologiques qui aboutirent à la disparition de la source principale de nourriture du hareng. Un stress environnemental très fort, joint à des pressions pour augmenter encore plus les prises, mena les stocks de harengs à l'effondrement. Siglufjörður se trouva tout d'abord marginalisé, puis, à mesure que le hareng disparaissait, carrément exclu. Durant les décennies suivant l'effondrement de 1968, cette ancienne ville champignon a tenté de trouver des solutions de rechange pour se développer de façon durable