VictorJuiz/thesis huggingface dataset:
The ice crystal-graupel collision charging mechanism of thunderstorm electrification
Keywords: Physics

The ice crystal-graupel collision charging mechanism, which is considered important in thunderstorm electrification, was studied using a newly developed Triple Interaction Facility. The facility is the first to allow independent control of the solid, liquid and vapor phases of a simulated cloud. The charge transferred to a riming target by collisions with ice crystals was measured over a wide range of cloud conditions. It was found that the charge transfer was a function of the temperature and the effective liquid water content of the cloud. It was also found that the charge transfer to the target was extremely sensitive to the relative humidity at which the ice crystals were grown. Higher relative humidity always promoted stronger negative charging, while lower humidity led to weaker negative or stronger positive charging. The sensitivity of the charge transfer to relative humidity was greatest at temperatures between-13°C and-18°C, with the strongest negative charging observed near-15°C. Within this temperature range the average charge transferred to the target could be varied from +5 fC per ice crystal collision to -25 fC per collision by varying the humidity from ice to water saturation, respectively. In experiments performed at humidities near water saturation and at temperatures near -15°C, charge transfers greater than -60 fC per collision were observed within the first 30 seconds after ice crystals are initiated. It was also found that at high relative humidity the maximum negative charge transferred to the target occurred at a velocity of 5m s-1 and was much weaker at 3, 4 and 6 m s-1. A parameterization of the results is presented for use in numerical thunderstorm models. Analysis of the data indicates that a competition between negative charge transfer between the liquid-like' layers of the colliding ice particles and positive charge transfer due to different dislocation densities can provide a consistent physical model of the effect of relative humidity. It is shown that differences in. the relative humidity can explain quantitatively the discrepancies between the observations of previous investigators. A new conceptual model of thunderstorm electrification is also presented.
Whole-rock dating of young extrusives by the potassium-argon method
Keywords: Physics

The feasibility of dating very young extrusives by the wholerock potassium-argon technique has been investigated. Rocks from the Columbia River Basalts, Oregon, Rio Grande de Santiago volcanics, Mexico, San Francisco Volcanic Field, Arizona, Hawaii and Australia have been studied. Some of the results point out the grave difficulties that can arise due to the presence of small quantities of excess argon in such rocks. ·Comparison on the ages of rocks in the age range 0 to 5 million years strongly suggest that inter-laboratory differences exist especially in the detection and measurement of small quantities of radiogenic argon. Study of a very thick extrusive of Recent age indicates that atmospheric argon may have been incorporated into the edges of the flow as it solidified. The quantity of argon present and its isotopic composition is not homogeneous throughout the lava flow. Wherever possible, the data are examined on potassium-argon isochrons. This yields information about the precision of the individual analyses. Lack of total control over the “blanks" during the argon analyses, does not allow unequivocal interpretation of the meaning of the "ages" obtained.
Magnetic Properties Of Deep-Ocean Basalts
Keywords: Physics

The deepest drill penetration ever into the oceanic crust was achieved during Legs 37 and 45 of the Deep Sea Drilling Program. In the present study, the magnetic properties of a large collection of basalt samples from Legs 37 and 45 near the Mid-Atlantic-Ridge were measured. Knowledge of these magnetic properties is of interest for two reasons: First, such information is required to understand and interpret features of the marine magnetic anomalies which are fundamental to the Vine and Matthews (1963) hypothesis. Regions of weak or absent magnetic anomalies and regions of enhanced anomalies may be explained by variations in magnetic properties. The second reason is that the ocean floor could provide an easily-dated record of the history of the earth's magnetic field. Oceanic basalts have proved too complex for blind application of paleo-intensity measurements. Knowledge of their magnetic properties would allow suitable samples to be selected. For the basalt samples, hysteresis parameters, coercive force, Hc, coercivity of remanence, Hcr, saturation magnetization, Js, remanent saturation magnetization, Jrs, and susceptibility were measured before and after heating. Curie temperatures, the stability of NRM to alternating fields and the importance of viscous magnetic components were also evaluated. It appears that most of the variation in magnetic properties can be attributed to changes in magnetic domain structure resulting from low-temperature oxidation of titanomagnetite to titanomaghemite. The magnetic properties measured before and after heating were used to develop .a set of criteria for choosing suitable samples for paleo-intensity estimates using the Thellier method. Only five samples from Leg 37 satisfied the criteria. These samples gave a paleo-intensity value of 0.53±.06 oe, close to the present day value. The rather complex behaviour of most samples upon heating is explained here by a two-stage unmixing process in which titanomaghemite first unmixes to a low-titanium, low—oxidation level titanomaghemite and a heme-ilmenite at about 300°C. Secondly, the titanomaghemite unmixes further to nearly pure magnetite. In addition, a number of explanations for the shallower-than-expected inclinations often observed in basalts from the Atlantic were considered. It is concluded that self-demagnetization of strongly magnetic lavas at the ridge axis and large tectonic rotations are the most likely explanations.
In-Vivo Neutron Activation Analysis And Associated Dosimetry
Keywords: Physics

The use of neutron activation analysis in vivo for the measurement of calcium in the human body has proved to be a more accurate and less hazardous technique than many other methods currently used. The health hazard associated with this technique is determined in this study by a method of neutron dosimetry, based on the radiation damage in plastics caused by neutron induced fission fragments…
Hail Formation And Its Effect On A Model Updraft
Keywords: Physics

The simulation of hailgrowth and its effects on cloud liquid water and energy balance is achieved by injecting hail embryos at the freezing level of a model updraft. Steady-state one-dimensional numerical models in which hail is only ascending or where it is ascending and descending are considered. The problems associated with the hail accumulation zones of former similar models are overcome by introducing a size distribution of hail embryos. Moderate concentrations of hail embryos, H to 2 per cubic meter, grow to deplete a significant fraction of the cloud's liquid water content. If this significant depletion of liquid water occurs, a hail accumulation zone is formed wherein the downward force on the cloud's updraft due to the hailstones is of the same order of magnitude as the upward buoyant force and further these zones are found to contain a maximum hail mass only three or four times greater than the vet-adiabatic liquid water content. The growth of hailstones from 0.25 or 0.50cm embryos to 3cm while ascending or U to 6cm after ascending and descending takes about lOmin in the former case and 20-30min in the latter. These growth rates are consistent with radar observations and they require only adiabatic liquid water contents (3*5gn/m* at maximum). Even larger stones are grown when they are non-spherical. The growth of large hailstones is therefore not dependent on an elaborate model of hailstone recycling within the cloud. Hail surface icing conditions and heat and mass exchange between the hailstones and the cloud air are found to be important to hailstone characteristics, the updraft's energy balance and liquid water content. Therefore, any future models of hailclouds should include the feedback mechanisms between growing hail and cloud air if moderate to heavy hail showers are to be numerically simulated. Altering the number of hail embryos or the cloud's liquid water content for the purpose of weather modification can produce positive or negative effects on hail production which are highly dependent on the hailcloud's parameters. For this reason any methods used to suppress hail should be allied with a definitive model of hail formation.
A study of the decay properties of the charmed baryon charmed positive lambda baryon
Keywords: Physics

The charmed baryon $\Lambda\sbsp{c}{+}$ has been observed using the ARGUS detector in the DORIS II $e\sp{+}e\sp-$ storage ring at DESY. The ARGUS experiment is a 4$\pi$ magnetic solenoidal detector used to observe $e\sp{+}e\sp-$ annihilations at center-of-mass energies around 10.4 GeV. We have studied 5 decays modes of the $\Lambda\sbsp{c}{+}$. The decay mode $\Lambda\sbsp{c}{+}\to pK\sp-\pi\sp+$ was used to measure the $\Lambda\sbsp{c}{+}$ fragmentation properties. A value of 0.24 $\pm$ 0.04 was found for the Peterson et al. parameter $\epsilon$, and the $\sigma(\Lambda\sbsp{c}{+}$) $\cdot\ BR(\Lambda\sbsp{c}{+}\to pK\sp-\pi\sp+$) was measured to be 12.0 $\pm$ 1.1 $\pm$ 1.3) pb. The decay modes $\Lambda\sbsp{c}{+}\to\Lambda\pi\sp+$ and $\Lambda\sbsp{c}{+}\to\Sigma\sp0\pi\sp+$ were also studied. In the former the asymmetry parameter $\alpha\sb{\Lambda\sb{c}}$ was measured to be $-$1.0 $\pm$ 0.5, indicating that parity is maximally violated in this decay. The two production cross section times branching ratios were measured to be (2.2 $\pm$ 0.3 $\pm$ 0.3) pb and (2.0 $\pm$ 0.7 $\pm$ 0.3) pb respectively. Finally, a search was made for evidence of W-exchange in the decay $\Lambda\sbsp{c}{+}\to\Xi\sp-K\sp+\pi\sp+$. This final state can arise through a simple spectator decay or via the more exotic W-exchange decay into $\Xi\sp{*0}K\sp+$, where the $\Xi\sp{*0}$ subsequently decays into $\Xi\sp-\pi\sp+$. The two body rate was measured to be (35 $\pm$ 17)% of the three body rate, indicating that a significant portion of the $\Xi\sp-K\sp+\pi\sp+$ final state may occur via W-exchange.
A theoretical roadmap for optical lithography of photonic band gap microchips
Keywords: Physics

This thesis presents designs and fabrication algorithms for 3D photonic band gap (PBG) material synthesis and embedded optical waveguide networks. These designs are suitable for large scale micro-fabrication using optical lithography methods. The first of these is a criss-crossing pore structure based on fabrication by direct photo-electrochemical etching in single-crystal silicon. We demonstrate that a modulation of the pore radius between pore crossing points leads to a moderately large PBG. We delineate a variety of PBG architectures amenable to fabrication by holographic lithography. In this technique, an optical interference pattern exposes a photo-sensitive material, leading to a template structure in the photoresist whose dielectricair interface corresponds to an iso-intensity surface in the exposing interference pattern. We demonstrate PBG architectures obtainable from the interference patterns from four independent beams. The PBG materials may be fabricated by replicating the developed photoresist with established silicon replication methods. We identify optical beam configurations that optimize the intensity contrast in the photoresist. We describe the invention of a new approach to holographic lithography of PBG materials using the diffraction of light through a three-layer optical phase mask (OPM). We show how the diffraction-interference pattern resulting from single beam illumination of our OPM closely resembles a diamondlike architecture for suitable designs of the phase mask. It is suggested that OPML may both simplify and supercede all previous optical lithography approaches to PBG material synthesis. Finally, we demonstrate theoretically the creation of three-dimensional optical waveguide networks in holographically defined PBG materials. This requires the combination of direct laser writing (DLW) of lines of defects within the holographically-defined photoresist and the replication of the microchip template with a high refractive index semiconductor such as silicon. We demonstrate broad-band (100-200 nm), single-mode waveguiding in air, based on the light localization mechanism of the PBG as well as sharp waveguide bends in three-dimensions with minimal backscattering. This provides a basis for broadband 3D integrated optics in holographically defined optical microchips.
Quasielastic proton spin transfer observations at intermediate energies
Keywords: Physics

Three sets of new data for inclusive quasielastic polarized proton scattering as presented. These include two complete sets of data for 12C at two incident proton kinetic energies 290 MeV and 420 MeV. The third is a partial set of spin observables for 16O at 420 MeV. The scattering angle at each energy is chosen for a central momentum-transfer of 1.9m-1 in the nucleon-nucleon frame, which corresponds to an energy-transfer of 80 MeV, well above the giant resonances, yet well below the Δ-isobar excitation. A Fermi-gas model is used to calculate the quasielastic spin observables across the full width of the quasielastic peak, and the longitudinal-to-transverse ratio of the spin-isospin nuclear response functions is extracted from the data. Our results indicate that the inclusive interaction is dominated by the nucleon-nucleon scattering process, but no enhancement of the longitudinal nuclear response is seen, contrary to the suggestions of spin-isospin collectivity in the nuclear interaction. Comparison of the 12C and 16O data reveals a remarkable resemblance of the respective spin observables, in support of the peripheral nature of inclusive proton scattering, and indicates that the inclusive quasielastic interaction is insensitive to nuclear structure. Effects of medium modification to the free nucleon-nucleon process, however, are evident in the pronounced quenching of the polarization parameter relative to the free value.
Linear and nonlinear optical processes in artificially structured materials
Keywords: Physics

We discuss optical effects in two channel micro-resonator structures, identify the underlying physics through a study of their dispersion relations, and present an efficient numerical technique that can be used to analyze pulse propagation within these structures when a Kerr nonlinearity is present. We show that these structures are ideal candidates for a number of photonic applications, such as optical buffers and optical AND-gates. The proposed applications are of interest to practitioners in the field of integrated optics. Following the discussion of numerical results, we present a Lorentzian model to describe transmission across short, Kerr nonlinear micro-resonator structures. Based on this model we derive a set of coupled differential equations that describe Kerr nonlinear pulse propagation and optical switching in systems coupled by a few cavities. The resulting equations greatly facilitate numerical investigations of intensity-dependent switching and optical bistability in such systems. We then consider a relation between the band structure and real space symmetry of a general class of quasi-lD dielectric structures. We show that by transforming the dielectric profile of these structures to an appropriate mirror image, time-reversed electromagnetic pulse propagation can be achieved. Our scheme provides a general recipe for obtaining time-reversed propagation in quasi-lD structures. In order to gain a deeper insight into pulse dynamics in periodic micro-resonator structures, we derive, for the first time, a set of coupled mode equations that describe pulse dynamics in the vicinity of the associated indirect band gaps. We employ an effective-field method and use a phenomenological Hamiltonian as the starting point. The resulting coupled mode equations are applicable to a wide class of side-coupled cavity structures, and lead to a more intuitive understanding of their dispersion relations. Lastly, we develop a rigorous Hamiltonian formulation for coupling problems commonly encountered in the study of artificially structured materials. We employ a "dressed mode" approach, which differs from coupled mode formalisms commonly used in the literature. The proposed formalism can be extended to include nonlinear effects in a systematic manner, and facilitate the analysis of optical processes in artificially structured materials in the quantum and nonlinear regimes.
Paleointensity determinations on basaltsfrom the Emperor Seamounts and testingthe properties of FORC diagrams usingmicromagnetic modelling and measurements
Keywords: Physics

The intensity of the geomagnetic field recorded in rocks from the Emperor Seamounts was measured. Paleolatitudes determined from thermal demagnetization in the Thellier experiments support the hypothesis of a moving Hawaiian hotspot. Because of thermal alteration and the presence of titanomaghemite, the Thellier success rate was only 5%. The virtual axial dipole moment at 56 Ma was (7.2 ± 0.2) x 1022 Am2 , about 60% higher than the average value for the 300-0.3 Ma time period, although still within the error bounds of this average. First-order reversal curve (FORC) diagrams give the coercivity and interaction field distributions of magnetic minerals and could be used to pre-select samples for paleointensity experiments. Micromagnetic modelling shows that non-interacting particles are manifested by a symmetrical single peak. When particles interact, splitting of the central peak on the interaction field (Hu) axis might explain the vertical spread observed on FORC diagrams. I measured FORC diagrams on elongated SD particles at temperatures ranging from 20 K to 853 K. The median field of the profile through the FORC peak along the coercivity field (Hu) axis varies in proportion to the bulk coercive force. The half-width of a profile through the FORC peak parallel to the Hu axis is similar to independent measures of local interaction fields Hi. These properties support the interpretation of the FORC variables He and Hu as being equivalent to microcoercivity He and interaction field Hi, respectively, and validate the FORC method. In nature, magnetic minerals usually occur as mixtures. The linear additivity of FORC diagrams was investigated, in order to study the possibility of separating magnetic mixtures into their components. Micromagnetic models of mixtures of magnetite and hematite and mixtures of magnetite with bimodal grain size distributions, as well as experimental measurements, yield linearly additive FORC diagrams. I compared FORC and Preisach diagrams measured on a range of natural and synthetic samples. I find a good agreement between both diagrams in the main features. Contours that are very close to the Hu axis are not imaged on a Preisach diagram. As a first approximation, FORC and Preisach diagrams are equivalent. However, the level of detail offered by FORC diagrams makes them more attractive to use than Preisach diagrams.
High Field Magnetic Properties Of Iron-Platinum Alloys In The Context Of The Invar Problem
Keywords: Physics

The magnetic properties of a series of f.c.c. Fe-Pt alloys, near Fe3Pt, have been investigated at low temperatures as a function of composition and atomic ordering. This thesis describes two aspects of such study. First, the design and construction of a new type of orbiting sample magnetometer of high sensitivity (Δx/x=4x10-3 ). This magnetometer permits the direct comparison of two samples (the ordered and disordered states at a given concentration) and a standard in a wide range of temperatures and magnetic fields. Second, the behaviour of Fe-Pt is characterized relative to that of the other Invars. In particular the similarities and differences with the classical Fe-Ni Invar are stressed. Central to the design of the magnetometer has been the development of bearings which can operate under the combined effects of high speed and low temperature in the presence of a high magnetic field. The sample holder consist of a horizontal wheel which is rotated in a vertical magnetic field. The three samples are passed successively through detection coils at a fixed frequency achieved by means of a phase sensitive feedback loop. The output signal contains all the information of the flux changes due to all three samples; this signal is processed by a signal averaging system...
Baryons In A Relativized Quark Model With QCD
Keywords: Physics

The three quark system is studied in a 'relativized' version of the quark model which incorporates the important features of quantum chromodynamics. These include a universal one-gluon exchange potential and a string picture confining potential. A good description is obtained of the masses and compositions of all the known baryons known baryons from the nucleon to the ∑e, with parameters similar to those of an analogous study of the qq system. The inclusion of relativistic effects leads to a natural explanation of the apparent absence of spin-orbit interactions in baryons, and is crucial to the success of the model. The results indicate that a well-founded and successful quark model can be built on the basis of the effects expected from QCD and from a relativistic treatment of the quark dynamics.
Moist potential vorticity generation in extratropical cyclones
Keywords: Physics

The mechanism of moist potential vorticity (MPV) generation in a three-dimensional moist adiabatic and frictionless flow is investigated. It is found that MPV generation is governed by baroclinic vectors and moisture gradients. Negative (positive) MPV can be generated in the region where baroclinic vectors have a component along (against) the direction of moisture gradients. Numerical simulations of extratropical cyclones with different moisture distributions show that at the different stages of cvclogenesis, negative MPV usually appears in the warm sector near the north part of the cold front, the bent-back warm front, the warm core and the cold front. The effects of the Boussinesq approximation on the distribution of vorticity and M PV are examined. The Boussinesq approximation neglects several components of the solenoidal term in the vorticity equation. As a result, it underestimates the thermally direct circulations in the cold front and the bent-back warm front by 25% to 30%. This effect is more pronounced when latent heat release is taken into account. Consequently, the influence of the Boussinesq approximation on the M PV field is very significant. Evidence of the presence of conditional symmetric instability in the negative MPV region of the extratropical cyclone is also presented.