Continuum mechanics at nanoscale. A tool to study trees' watering and recovery

The cohesion-tension theory expounds the crude sap ascent thanks to the negative pressure generated by evaporation of water from leaves. Nevertheless, trees pose multiple challenges and seem to live in unphysical conditions: the negative pressure increases cavitation; it is possible to obtain a water equilibrium between connected parts where one is at a positive pressure and the other one is at negative pressure; no theory is able to satisfactorily account for the refilling of vessels after embolism events. A theoretical form of our paper in the Journal of Theoretical Biology is proposed together with new results: a continuum mechanics model of the disjoining pressure concept refers to the Derjaguin School of physical chemistry. A comparison between liquid behaviour both in tight-filled microtubes and in liquid thin-films is offered when the pressure is negative in liquid bulks and is positive in liquid thin-films and vapour bulks. In embolized xylem microtubes, when the air-vapour pocket pressure is greater than the air-vapour bulk pressure, a refilling flow occurs between the air-vapour domains to empty the air-vapour pockets although the liquid-bulk pressure remains negative. The model has a limit of validity taking the maximal size of trees into account. These results drop inkling that the disjoining pressure is an efficient tool to study biological liquids in contact with substrates at a nanoscale range.Comment: The paper is a review and overlap of my different papers about the watering of trees as a mathematical development of my paper in The Journal of Theoretical Biology. These results are presented together with new researches: transfer of liquid water and vapour between xylem microtubes, an explanation of ultrasounds generated in the watering network considered as sound pipes, numerical calculations of flows in thin liquid films and of Poiseuille flows in xylem microtubes, an estimation of the velocity for the ascent of crude sap and of the recovery time of trees during the spring perio

Grinding Temperature Measurements in Magnesia-Partially-Stabilized Zirconia Using Infrared Spectrometry

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65185/1/j.1151-2916.2003.tb00019.x.pd

Fracture aperture profiles as indicators of fracture growth environments : an integrated study of fracture aperture growth in the Campito Formation of eastern California

Processes of fracture formation control flow of fluid in the subsurface and the mechanical properties of the brittle crust. I investigate whether fracture aperture profiles describing the opening displacement along their height or length reflect fracture growth conditions and mechanisms. I hypothesize that aperture profiles of fractures growing under different environments and by different mechanisms have different ellipticity. I measured fracture profiles for quartz cemented opening-mode fractures in low-grade metamorphic sandstone of the Campito Formation, eastern California, and quantified their ellipticity using curve fitting methods based on the Lamé function. I compare the Lamé parameter n against structural and inferred environmental parameters, including fracture orientation, fracture tip characteristics, locations of fracture tips relative to layer boundaries, texture of fracture cements, and temperature during fracture growth as determined through fluid inclusion homogenization temperatures. Lamé n values range from 0.72 to 3.20, with the majority falling between 1 and 1.5. Fracture with n < 2 correlate with higher fluid inclusion homogenization temperatures between 270°C and 315°C, and are preferentially filled with blocky quartz cement. Fractures with fluid inclusion temperatures in the range of 150°C and 250°C have n~ 2 and preferentially contain crack-seal quartz cement. I observe no correlation between n and fracture orientation, and aperture/length ratio, although fractures with wide apertures have n<2. To explain fractures with n2 require opening increments with blunt tips and slow length or height growth relative to aperture growth. Our model is consistent with faster length growth resulting from reduced fracture toughness with increasing temperature, leading to low n at higher temperatures. The absence of crack-seal cement in fractures with low n may relate to overall fast fracture growth at higher temperatures, with aperture growth exceeding rates of synkinematic crack-seal quartz cementation. Fractures with n>2 require tip blunting that I attribute to enhanced solution-precipitation creep by stress concentration at the fracture tip.Geological Science

Photo-Emission Electron Microscopy (PEEM) Heating Investigations of a Natural Amphibole Sample

PEEM allows ‘real-time’ observations to be made of solid-state transformations and other high-temperature processes taking place during vacuum-heating up to c. 2000°C The solid state transformations of an amphibole-rich hornblendite specimen have been observed in the temperature range of 750–1000°C (± 50°C Between c. 970–990°C a rapid change in orientation contrast was observed, indicating a structural rearrangement from an oxyhornblende crystal lattice to a clinopyroxene structure. This phase retains the original amphibole shape and texture (including two 120°C intersecting cleavage traces), but possesses a clinopyroxene crystal structure. At higher temperatures this phase is seen to decompose, forming iron oxides and other fine-grained products. PEEM has provided useful information on both the nature and rates of transformation of natural amphiboles which has proved invaluable in our understanding of the mineralogically-controlled mechanisms of argon release during 40Ar/39Ar dating of amphibole samples

The Effect of Phase Constitution and Morphology on Room Temperature Deformation Behavior of Binary Titanium Alloys

Currently, titanium alloys are used in a variety of applications, including defense, aerospace, biomedicine, and even common consumer products such as bicycles and golf clubs. In many applications such as the landing gear of aircraft and geothermal energy production, titanium components may be subjected to stresses for extended periods of time. It has long been known that single-phase &alpha; (HCP), single-phase &beta; (BCC), and two-phase &alpha; + &beta; Ti alloys can creep at low temperatures (<0.25Tm). For this reason, creep is an important factor to consider when designing titanium alloys for various applications. The first part of this investigation is concerned with single-phase &alpha;-Ti alloys. It was found that the twin size (lamellar thickness) decreases with an increase in strain rate. This behavior is unexpected based on the classical understanding of instantaneous twinning. This investigation was able to for the first time demonstrate a time-dependent twinning phenomenon during high strain rate tensile deformation. The second part of this investigation is concerned with experimentally and theoretically studying low-temperature creep deformation behavior of two-phase &alpha; + &beta; Ti alloys. Deformation mechanisms were seen in two-phase &alpha; + &beta; Ti alloys that are not present during creep of the respective single-phase alloys with compositions equivalent to the individual phases. To investigate the possible interphase interaction stresses, 3D anisotropic Finite element modeling (FEM) was used. These simulations revealed that due to the Burgers orientation relationship between the two phases, deformation such as slip or twinning in the &alpha; phase can create very high additional shear stresses on different slip systems in the &beta; phase. This work also revealed that the interfacial stresses that develop between the two phases during elastic deformation will often be much greater than the applied stress. These results were used to help explain the additional deformation mechanisms seen in two-phase alloys that are not seen in the respective single-phase alloys during creep. This work was supported by the National Science Foundation under Grant Number DMR-0906994

Using Micro-Scale Observations to Understand Large-Scale Geophysical Phenomena: Examples from Seismology and Mineral Physics

abstract: Earthquake faulting and the dynamics of subducting lithosphere are among the frontiers of geophysics. Exploring the nature, cause, and implications of geophysical phenomena requires multidisciplinary investigations focused at a range of spatial scales. Within this dissertation, I present studies of micro-scale processes using observational seismology and experimental mineral physics to provide important constraints on models for a range of large-scale geophysical phenomena within the crust and mantle. The Great Basin (GB) in the western U.S. is part of the diffuse North American-Pacific plate boundary. The interior of the GB occasionally produces large earthquakes, yet the current distribution of regional seismic networks poorly samples it. The EarthScope USArray Transportable Array provides unprecedented station density and data quality for the central GB. I use this dataset to develop an earthquake catalog for the region that is complete to M 1.5. The catalog contains small-magnitude seismicity throughout the interior of the GB. The spatial distribution of earthquakes is consistent with recent regional geodetic studies, confirming that the interior of the GB is actively deforming everywhere and all the time. Additionally, improved event detection thresholds reveal that swarms of temporally-clustered repeating earthquakes occur throughout the GB. The swarms are not associated with active volcanism or other swarm triggering mechanisms, and therefore, may represent a common fault behavior. Enstatite (Mg,Fe)SiO3 is the second most abundant mineral within subducting lithosphere. Previous studies suggest that metastable enstatite within subducting slabs may persist to the base of the mantle transition zone (MTZ) before transforming to high-pressure polymorphs. The metastable persistence of enstatite has been proposed as a potential cause for both deep-focus earthquakes and the stagnation of slabs at the base of the MTZ. I show that natural Al- and Fe-bearing enstatite reacts more readily than previous studies and by multiple transformation mechanisms at conditions as low as 1200°C and 18 GPa. Metastable enstatite is thus unlikely to survive to the base of the MTZ. Additionally, coherent growth of akimotoite and other high-pressure phases along polysynthetic twin boundaries provides a mechanism for the inheritance of crystallographic preferred orientation from previously deformed enstatite-bearing rocks within subducting slabs.Dissertation/ThesisGreat Basin Seismicity from 2004 to 2013 (event data)Great Basin Seismicity from 2004 to 2013 (Google Earth)Doctoral Dissertation Geological Sciences 201

Digital Background Self-Calibration Technique for Compensating Transition Offsets in Reference-less Flash ADCs

This Dissertation focusses on proving that background calibration using adaptive algorithms are low-cost, stable and effective methods for obtaining high accuracy in flash A/D converters. An integrated reference-less 3-bit flash ADC circuit has been successfully designed and taped out in UMC 180 nm CMOS technology in order to prove the efficiency of our proposed background calibration. References for ADC transitions have been virtually implemented built-in in the comparators dynamic-latch topology by a controlled mismatch added to each comparator input front-end. An external very simple DAC block (calibration bank) allows control the quantity of mismatch added in each comparator front-end and, therefore, compensate the offset of its effective transition with respect to the nominal value. In order to assist to the estimation of the offset of the prototype comparators, an auxiliary A/D converter with higher resolution and lower conversion speed than the flash ADC is used: a 6-bit capacitive-DAC SAR type. Special care in synchronization of analogue sampling instant in both ADCs has been taken into account. In this thesis, a criterion to identify the optimum parameters of the flash ADC design with adaptive background calibration has been set. With this criterion, the best choice for dynamic latch architecture, calibration bank resolution and flash ADC resolution are selected. The performance of the calibration algorithm have been tested, providing great programmability to the digital processor that implements the algorithm, allowing to choose the algorithm limits, accuracy and quantization errors in the arithmetic. Further, systematic controlled offset can be forced in the comparators of the flash ADC in order to have a more exhaustive test of calibration