Modeling the electromagnetic properties of the SCUBA-2 detectors

SCUBA-2 is the next-generation replacement for SCUBA (Sub-millimetre Common User Bolometer Array) on the James Clerk Maxwell Telescope. Operating at 450 and 850 microns, SCUBA-2 fills the focal plane of the telescope with fully-sampled, monolithic bolometer arrays. Each SCUBA-2 pixel uses a quarter-wave slab of silicon with an implanted resistive layer and backshort as an absorber and a superconducting transition edge sensor as a thermometer. In order to verify and optimize the pixel design, we have investigated the electromagnetic behaviour of the detectors, using both a simple transmission-line model and Ansoft HFSS, a finite-element electromagnetic simulator. We used the transmission line model to fit transmission measurements of doped wafers and determined the correct implant dose for the absorbing layer. The more detailed HFSS modelling yielded some unexpected results which led us to modify the pixel design. We also verified that the detectors suffered little loss of sensitivity for off-axis angles up to about 30 degrees.Comment: 13 pages, 14 figures, SPIE Glasgow 21-25 June 2004, Conference 549

Strain control of ferromagnetic thin films and devices

Magnetic memory and logic technologies promise greater energy efficiency and speed than conventional, semiconductor-based electronics. To date, electrical current has been used to operate such devices, although voltage-control may be a more efficient way to control magnetisation. One route to achieving voltage control of magnetisation is to use a hybrid piezoelectric/ferromagnetic device in which a voltage applied to the piezoelectric induces a strain in the ferromagnetic layer, which in turn induces a magnetic anisotropy. In this thesis such hybrid devices are used to investigate the control of magnetisation by inducing uniaxial anisotropy in the ferromagnetic layer. One material that shows promise for use as the ferromagnetic layer is Fe81Ga19. This material is attractive since it contains no rare earth elements, and in bulk crystals has been shown to be highly magnetically responsive to strain. This thesis investigates the magnetic properties of epitaxial Fe81Ga19 thin films grown by molecular beam epitaxy and it is demonstrated that these thin films retain the attractive magnetostrictive properties previously observed in bulk crystals. The presence of strong cubic magnetocrystalline anisotropy in the layers is exploited to demonstrate the non-volatile switching of magnetisation using strain-induced anisotropy in the absence of an applied magnetic field. This thesis shows also the manipulation of magnetic anisotropies and control of the configuration of magnetic domains and domain walls in Fe81Ga19 at a range of different lateral dimensions, from50 μm to 1 μm. It is shown that as the lateral dimensions of the device structures studied are reduced the domain configuration appears more regular, and that strain-induced anisotropy is more able to control these domains. In wires around 1 μm in width it is shown that growth strain relaxation by lithographic patterning induces sufficient anisotropy to cause a change in the domain configuration of the wire studied. Finally, this thesis begins to investigate how inverse magnetostriction can be used to tune the behaviour of domain walls in wires 1 μm wide and narrower. Experimental control of the field required to depin a vortex domain wall from a notch in a 1 μm wide Co wire is demonstrated. Using micromagnetic simulations it is shown that a large degree of control over the depinning of domain walls from notches in wires 1 μm wide and narrower is possible. The influence of in plane uniaxial magnetic anisotropy on the domain wall velocity in wires supporting in plane transverse domain walls driven by an external magnetic field is also investigated. Work previously done on the effect of uniaxial anisotropy on domain wall velocities close to Walker breakdown is extended in this thesis and in investigating the velocity and structure at driving magnetic fields far above walker Breakdown a second peak in domain wall velocity is observed, a phenomenon previously observed in wide wires, and wires under the influence of a transverse magnetic field

Monoid presentations of groups by finite special string-rewriting systems

We show that the class of groups which have monoid presentations by means of finite special [λ]-confluent string-rewriting systems strictly contains the class of plain groups (the groups which are free products of a finitely generated free group and finitely many finite groups), and that any group which has an infinite cyclic central subgroup can be presented by such a string-rewriting system if and only if it is the direct product of an infinite cyclic group and a finite cyclic group

Strain control of ferromagnetic thin films and devices

Magnetic memory and logic technologies promise greater energy efficiency and speed than conventional, semiconductor-based electronics. To date, electrical current has been used to operate such devices, although voltage-control may be a more efficient way to control magnetisation. One route to achieving voltage control of magnetisation is to use a hybrid piezoelectric/ferromagnetic device in which a voltage applied to the piezoelectric induces a strain in the ferromagnetic layer, which in turn induces a magnetic anisotropy. In this thesis such hybrid devices are used to investigate the control of magnetisation by inducing uniaxial anisotropy in the ferromagnetic layer. One material that shows promise for use as the ferromagnetic layer is Fe81Ga19. This material is attractive since it contains no rare earth elements, and in bulk crystals has been shown to be highly magnetically responsive to strain. This thesis investigates the magnetic properties of epitaxial Fe81Ga19 thin films grown by molecular beam epitaxy and it is demonstrated that these thin films retain the attractive magnetostrictive properties previously observed in bulk crystals. The presence of strong cubic magnetocrystalline anisotropy in the layers is exploited to demonstrate the non-volatile switching of magnetisation using strain-induced anisotropy in the absence of an applied magnetic field. This thesis shows also the manipulation of magnetic anisotropies and control of the configuration of magnetic domains and domain walls in Fe81Ga19 at a range of different lateral dimensions, from50 μm to 1 μm. It is shown that as the lateral dimensions of the device structures studied are reduced the domain configuration appears more regular, and that strain-induced anisotropy is more able to control these domains. In wires around 1 μm in width it is shown that growth strain relaxation by lithographic patterning induces sufficient anisotropy to cause a change in the domain configuration of the wire studied. Finally, this thesis begins to investigate how inverse magnetostriction can be used to tune the behaviour of domain walls in wires 1 μm wide and narrower. Experimental control of the field required to depin a vortex domain wall from a notch in a 1 μm wide Co wire is demonstrated. Using micromagnetic simulations it is shown that a large degree of control over the depinning of domain walls from notches in wires 1 μm wide and narrower is possible. The influence of in plane uniaxial magnetic anisotropy on the domain wall velocity in wires supporting in plane transverse domain walls driven by an external magnetic field is also investigated. Work previously done on the effect of uniaxial anisotropy on domain wall velocities close to Walker breakdown is extended in this thesis and in investigating the velocity and structure at driving magnetic fields far above walker Breakdown a second peak in domain wall velocity is observed, a phenomenon previously observed in wide wires, and wires under the influence of a transverse magnetic field

Hyaluronan and Collagen Are Prominent Extracellular Matrix Components in Bovine and Porcine Ovaries

A grant from the One-University Open Access Fund at the University of Kansas was used to defray the author's publication fees in this Open Access journal. The Open Access Fund, administered by librarians from the KU, KU Law, and KUMC libraries, is made possible by contributions from the offices of KU Provost, KU Vice Chancellor for Research & Graduate Studies, and KUMC Vice Chancellor for Research. For more information about the Open Access Fund, please see http://library.kumc.edu/authors-fund.xml.The extracellular matrix (ECM) is a major component of the ovarian stroma. Collagen and hyaluronan (HA) are critical ovarian stromal ECM molecules that undergo age-dependent changes in the mouse and human. How these matrix components are regulated and organized in other mammalian species with reproductive characteristics similar to women such as cows and pigs, has not been systematically investigated. Therefore, we performed histological, molecular, and biochemical analyses to characterize collagen and HA in these animals. Bovine ovaries had more collagen than porcine ovaries when assessed biochemically, and this was associated with species-specific differences in collagen gene transcripts: Col3a1 was predominant in cow ovaries while Col1a1 was predominant in pig ovaries. We also observed more HA in the porcine vs. bovine ovary. HA was distributed across three molecular weight ranges (300 kDa) in ovarian tissue and follicular fluid, with tissue having more >300 kDa HA than the other two ranges. Transcripts for HA synthesis and degradation enzymes, Has3 and Hyal2, respectively, were predominant in cow ovaries, whereas Has2, Kiaa1199, and Tmem2 tended to be predominant in pig ovaries. Together, our findings have implications for the composition, organization, and regulation of the ovarian ECM in large mammalian species, including humans

Short and long-read genome sequencing methodologies for somatic variant detection; genomic analysis of a patient with diffuse large B-cell lymphoma

Recent advances in throughput and accuracy mean that the Oxford Nanopore Technologies PromethiON platform is a now a viable solution for genome sequencing. Much of the validation of bioinformatic tools for this long-read data has focussed on calling germline variants (including structural variants). Somatic variants are outnumbered many-fold by germline variants and their detection is further complicated by the effects of tumour purity/subclonality. Here, we evaluate the extent to which Nanopore sequencing enables detection and analysis of somatic variation. We do this through sequencing tumour and germline genomes for a patient with diffuse B-cell lymphoma and comparing results with 150 bp short-read sequencing of the same samples. Calling germline single nucleotide variants (SNVs) from specific chromosomes of the long-read data achieved good specificity and sensitivity. However, results of somatic SNV calling highlight the need for the development of specialised joint calling algorithms. We find the comparative genome-wide performance of different tools varies significantly between structural variant types, and suggest long reads are especially advantageous for calling large somatic deletions and duplications. Finally, we highlight the utility of long reads for phasing clinically relevant variants, confirming that a somatic 1.6 Mb deletion and a p.(Arg249Met) mutation involving TP53 are oriented in trans

Finite Theories and the SUSY Flavor Problem

We study a finite SU(5) grand unified model based on the non-Abelian discrete symmetry A_4. This model leads to the democratic structure of the mass matrices for the quarks and leptons. In the soft supersymmetry breaking sector, the scalar trilinear couplings are aligned and the soft scalar masses are degenerate, thus solving the SUSY flavor problem.Comment: 17 pages, LaTeX, 1 figur

A knee brace alters patella position in patellofemoral osteoarthritis: A study using weight bearing magnetic resonance imaging.

OBJECTIVE: To assess using weight bearing MRIs, whether a patellar brace altered patellar position and alignment in patellofemoral joint (PFJ) osteoarthritis (OA). DESIGN: Subjects age 40-70 years old with symptomatic and a radiographic K-L evidence of PFJOA. Weight bearing knee MRIs with and without a patellar brace were obtained using an upright open 0.25 Tesla scanner (G-Scan, Easote Biomedica, Italy). Five aspects of patellar position were measured: mediolateral alignment by the bisect offset index, angulation by patellar tilt, patellar height by patellar height ratio (patellar length/patellar tendon length), lateral patellofemoral contact area and finally a measurement of patellofemoral bony separation of the lateral patellar facet and the adjacent surface on the femoral trochlea (Figure 1). RESULTS: Thirty participants were recruited (mean age 57 SD 27.8; BMI 27.8 SD 4.2); 17 were females. Four patients had non-usable data. Main analysis used paired t tests comparing within subject patellar position with and without brace. For bisect offset index, patellar tilt and patellar height ratio there were no significant differences between the brace and no brace conditions. However, the brace increased lateral facet contact area (p =.04) and decreased lateral patellofemoral separation (p = .03). CONCLUSION: A patellar brace alters patellar position and increases contact area between the patella and femoral trochlea. These changes would lower contact stress at the PFJ. Such changes in patella position in weight bearing provide a possible biomechanical explanation for the success of the PFJ brace in clinical trials on PFJOA