Comparison of forest attributes derived from two terrestrial lidar systems.

Abstract Terrestrial lidar (TLS) is an emerging technology for deriving forest attributes, including conventional inventory and canopy characterizations. However, little is known about the influence of scanner specifications on derived forest parameters. We compared two TLS systems at two sites in British Columbia. Common scanning benchmarks and identical algorithms were used to obtain estimates of tree diameter, position, and canopy characteristics. Visualization of range images and point clouds showed clear differences, even though both scanners were relatively high-resolution instruments. These translated into quantifiable differences in impulse penetration, characterization of stems and crowns far from the scan location, and gap fraction. Differences between scanners in estimates of effective plant area index were greater than differences between sites. Both scanners provided a detailed digital model of forest structure, and gross structural characterizations (including crown dimensions and position) were relatively robust; but comparison of canopy density metrics may require consideration of scanner attributes

Streaking images that appear only in the plane of diffraction in undoped GaAs single crystals: Diffraction imaging (topography) by monochromatic synchrotron radiation

Streaking images restricted to the direction of the diffraction (scattering) vector have been observed on transmission through undoped GaAs. These disruption images (caused by the reduction of diffraction in the direction of observation) appear both in the forward and in Bragg diffracted directions in monochromatic synchrontron radiation diffraction imaging. This previously unobserved phenomenon can be explained in terms of planar defects (interfaces) or platelets which affects the absorption coefficient in anomalous transmission. Such regions of the crystal look perfect despite the presence of imperfections when the scattering vector is not perpendicular to the normal of the platelets. The observed crystallographic orientation of these interfaces strongly indicates that they are antiphase boundaries

Design considerations for minimizing noise in micropower CMOS integrated circuits

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996.Includes bibliographical references (p. 70-72).by Bruce C. Larson.M.S

An optical telemetry system for wireless transmission of biomedical signals across the skin

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Vita.Includes bibliographical references (p. 236-239).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.A technology base for optically-coupled systems was developed that permits in-vivo transmission of biomedical signals across the skin. By complete implantation of sensors and instrumentation electronics, problems with percutaneous connectors were eliminated. Optical power and signal transmission was accomplished with smaller and lighter implant structures than previously achieved with radio frequency (RF) coupling techniques. This is particularly valuable in the field of neuroprosthetics, because it may be possible to implant an optical telemeter directly on the surface of the brain to make mechanically stable connections to microelectrode arrays for neuroelectric recordings. Miniature optical power panels (2.5 mm x 2.5 mm) were developed from arrays of photodiodes. Infrared light of 880 nm wavelength was effective for delivering power across the skin. Panels composed of silicon photodiodes were 14% efficient at converting this light to electrical power, and GaAlAs panels were 41% efficient. Tissue heating experiments demonstrated the safety of optical power transmission. An LED was identified that was both electrically efficient (16%) and of appropriate wavelength (660 nm) for transmitting optical signals from the implant. Pulse period encoding was used for transmission of signals because it was robust and required less power than schemes with higher LED duty cycles. Specialized photodetector circuits were developed to receive pulse encoded data, and decoder circuits were built to reconstruct the transmitted signals. Two prototype single-channel neural waveform telemeters (approx. 10 Hz to 7 kHz bandwidth) were constructed and implanted in the visual cortex of rabbits. Both implants successfully transmitted neuroelectric signals. The first implant survived for four weeks before failing due to a flaw in the encapsulation, and the improved second prototype continues to function properly 28 months after implantation. Integrated circuits (ICs) were designed to record and transmit eight channels of neural waveforms. The first IC telemeter functioned properly, although the sensitivity was not as great as needed for the recording of neural waveforms. It required less than 50 mW of electrical power to operate. Efforts to improve this design introduced flaws in the next set of IC designs, so these problems were addressed, and a final set of designs was submitted for fabrication at the conclusion of this research project.by Bruce C. Larson.Ph.D

Temporal patterns of radial growth in declining Austrocedrus chilensis forests in Northern Patagonia: The use of tree-rings as an indicator of forest decline

Using dendrochronology, combined with tree- and stand-level information, we reconstructed the temporal dynamics of ‘mal del ciprés’, a widespread decline of Austrocedrus chilensis forests in Argentina. We developed 12 new site-specific ring-width chronologies representing the growth of trees with no external (crown) or internal (radial growth) symptoms of decline. By comparing the ring-width series of individual trees with these reference chronologies, we detected reduced radial growth, likely due to ‘mal del ciprés’, in 301 symptomatic and dead overstory trees out of 1082 sampled trees. Radial growth decline also occurred in 67 living trees with asymptomatic crowns providing evidence that radial growth decline can be an early indicator of ‘mal del ciprés’. The length of the radial growth decline averaged 27 years for all trees and was 29 and 22 years for living symptomatic and dead overstory trees, respectively; the maximum decline length was 80 years. At the site level, the onset of radial growth decline ranged from the early 1920s to the 1960s, preceding dates reported in historical records. By 1979, P75% of trees per site exhibited radial growth decline. We conclude that decline in radial growth precedes crown symptoms in at least some A. chilensis trees in forests with ‘mal del ciprés’. Reduced radial growth prior to external crown symptoms implies that water uptake had been reduced, possibly because of root damage from Phyophthora or drought or their interactions. It also suggests salvage harvests that aim to eradicate trees with crown symptoms and facilitate growth of residual trees may not be the most effective management response to ‘mal del ciprés’.Fil: Amoroso, Mariano Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Daniels, Lori D.. University of British Columbia; CanadáFil: Larson, Bruce C.. University of British Columbia; Canad

A Prediction of Brown Dwarfs in Ultracold Molecular Gas

A recent model for the stellar initial mass function (IMF), in which the stellar masses are randomly sampled down to the thermal Jeans mass from hierarchically structured pre-stellar clouds, predicts that regions of ultra-cold CO gas, such as those recently found in nearby galaxies by Allen and collaborators, should make an abundance of Brown Dwarfs with relatively few normal stars. This result comes from the low value of the thermal Jeans mass, considering that the hierarchical cloud model always gives the Salpeter IMF slope above this lower mass limit. The ultracold CO clouds in the inner disk of M31 have T~3K and pressures that are probably 10 times higher than in the solar neighborhood. This gives a mass at the peak of the IMF equal to 0.01 Msun, well below the Brown Dwarf limit of 0.08 Msun. Using a functional approximation to the IMF, the ultracold clouds would have 50% of the star-like mass and 90% of the objects below the Brown Dwarf limit. The brightest of the Brown Dwarfs in M31 should have an apparent, extinction-corrected K-band magnitude of ~21 mag in their pre-main sequence phase.Comment: 13 pages, 2 figures, to be published in Astrophysical Journal, Vol 522, September 10, 199

Engineering a catabolic pathway in plants for the degradation of 1,2-dichloroethane

Plants are increasingly being employed to clean up environmental pollutants such as heavy metals; however, a major limitation of phytoremediation is the inability of plants to mineralize most organic pollutants. A key component of organic pollutants is halogenated aliphatic compounds that include 1,2-dichloroethane (1,2-DCA). Although plants lack the enzymatic activity required to metabolize this compound, two bacterial enzymes, haloalkane dehalogenase (DhlA) and haloacid dehalogenase (DhlB) from the bacterium Xanthobacter autotrophicus GJ10, have the ability to dehalogenate a range of halogenated aliphatics, including 1,2-DCA. We have engineered the dhlA and dhlB genes into tobacco (Nicotiana tabacum ‘Xanthi’) plants and used 1,2-DCA as a model substrate to demonstrate the ability of the transgenic tobacco to remediate a range of halogenated, aliphatic hydrocarbons. DhlA converts 1,2-DCA to 2-chloroethanol, which is then metabolized to the phytotoxic 2-chloroacetaldehyde, then chloroacetic acid, by endogenous plant alcohol dehydrogenase and aldehyde dehydrogenase activities, respectively. Chloroacetic acid is dehalogenated by DhlB to produce the glyoxylate cycle intermediate glycolate. Plants expressing only DhlA produced phytotoxic levels of chlorinated intermediates and died, while plants expressing DhlA together with DhlB thrived at levels of 1,2-DCA that were toxic to DhlA-expressing plants. This represents a significant advance in the development of a low-cost phytoremediation approach toward the clean-up of halogenated organic pollutants from contaminated soil and groundwater

In Solidarity

This edition of Next Page is a departure from our usual question and answer format with a featured campus reader. Instead, we asked speakers who participated in the College’s recent Student Solidarity Rally (March 1, 2017) to recommend readings that might further our understanding of the topics on which they spoke

The Predicting Tree Growth App: an algorithmic approach to modelling individual tree growth

PredictingTreeGrowth is free and open-source application software written in Python 3.7 that allows easy and fast development of predictive models using the Recurrent Neural Network (RNN)/Long Short-Term Memory (LSTM) framework. RNNs have an upgraded architecture able to capture tree growth mechanisms related to time ordering and size dependence. The motivation for this App is to demystify the use of Machine Learning algorithms and allow accessibility of Machine Learning algorithms by the scientific community. Its simple graphical user interface (GUI) provides straightforward tools for building predictive models with the RNN algorithm.Fil: Magalhaes, Juliana G. de S.. University of British Columbia; CanadáFil: Polinko, Adam P.. Mississippi State University.; Estados UnidosFil: Amoroso, Mariano Martin. Universidad Nacional de Río Negro. Sede Andina. Instituto de Investigaciones en Recursos Naturales, Agroecología y Desarrollo Rural; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Kohli, Gursimran S.. University Fraser Simon; CanadáFil: Larson, Bruce C.. University of British Columbia; Canad

Drought Management Concepts: Lessons of the 1976-1977 U.S. Drought

Three approaches to drought management are developed as generalized mathematical models. Each model is then applied to particular locations in Utah using the hydrologic/economic data from the 1976-77 drought. The modeling approaches include: (1) A multiple regression approach is used to quantify the changes in water use achieved by three common municipal sector rationing policies: (a) restrictions on time of outdoor use, (b) price increases, and (c) mandatory quantity restrictions (2) A model was presented for determing the optimal long term price schedule for rationing a stochastically variable water supply during summer peak demand season among groups of municipal water users which have different demands. (3) The third model analyzed various management policies in terms of their impact on net benefits to the agricultural and municipal sectors. The model is capable of modifying policies monthly, based upon the chaning hydrologic situation. It can vary constraints in a manner that simulates an institutional environment ranging from total freedom of price changes and water exchanges between sectors to those constraints existing during the 76-77 drought. Conclusions include: 1) Mandatory water use regulations are much more effective than price increases in reducing water use (at least in a short term drought). 2) A theoretical analysis of demand and supply functions showed that Salt Lake City\u27s pricing polity (about $0.25/1000 gallons) is very close to optimal. 3) The third model showed that very substantial losses in consumer surplus in Slat Lake County during the drought were caused by variuos institutional restrictions