443 research outputs found
An exactly solvable limit of low energy QCD
Starting from the QCD Hamiltonian, we derive a schematic Hamiltonian for low
energy quark dynamics with quarks restricted to the lowest s-level. The
resulting eigenvalue problem can be solved analytically. Even though the
Hamiltonian exhibits explicit chiral symmetry the severe restriction of the
number of degrees of freedom breaks the pattern of chiral symmetry breaking for
finite quark masses.Comment: 7 page
Electrostatic Modulation of the Electronic Properties of Dirac Semimetal Na3Bi
Large-area thin films of topological Dirac semimetal NaBi are grown on
amorphous SiO:Si substrates to realise a field-effect transistor with the
doped Si acting as back gate. As-grown films show charge carrier mobilities
exceeding 7,000 cm/Vs and carrier densities below 3 10
cm, comparable to the best thin-film NaBi. An ambipolar field effect
and minimum conductivity are observed, characteristic of Dirac electronic
systems. The results are quantitatively understood within a model of
disorder-induced charge inhomogeneity in topological Dirac semimetals. Due to
the inverted band structure, the hole mobility is significantly larger than the
electron mobility in NaBi, and when present, these holes dominate the
transport properties.Comment: 5 pages, 4 figures; minor corrections and revisions for readabilit
Confederate Wooden Gunboat Construction : Logistical Nightmare
The Confederate States Navy built wooden gunboats throughout the American Civil War. Within Civil War literature, more research and detailed analysis of Confederate States Navy construction focuses on building of ironclad vessels. Wooden gunboat construction is largely ignored. This thesis examines wooden gunboat construction in two different areas of the Confederacy: northeastern North Carolina in Washington and Elizabeth City, and the Mars Bluff Navy Yard in South Carolina. Before presenting two Confederate wooden gunboat construction case studies, a look at Confederate industrial, manufacturing, and transportation infrastructure, from the national perspective, brings into focus the logistical limitations station commanders faced in northeastern North Carolina and at Mars Bluff more clearly. Scattered, yet interdependent, marine manufacturing and ordnance facilities, connected by a suspect transportation network, created a logistical nightmare. Historical investigation into wooden gunboat construction in Washington, Elizabeth City, and Mars Bluff, examines an overlooked Confederate States Navy building program.  M.A
Towards practical classical processing for the surface code: timing analysis
Topological quantum error correction codes have high thresholds and are well
suited to physical implementation. The minimum weight perfect matching
algorithm can be used to efficiently handle errors in such codes. We perform a
timing analysis of our current implementation of the minimum weight perfect
matching algorithm. Our implementation performs the classical processing
associated with an nxn lattice of qubits realizing a square surface code
storing a single logical qubit of information in a fault-tolerant manner. We
empirically demonstrate that our implementation requires only O(n^2) average
time per round of error correction for code distances ranging from 4 to 512 and
a range of depolarizing error rates. We also describe tests we have performed
to verify that it always obtains a true minimum weight perfect matching.Comment: 13 pages, 13 figures, version accepted for publicatio
Towards practical classical processing for the surface code
The surface code is unarguably the leading quantum error correction code for
2-D nearest neighbor architectures, featuring a high threshold error rate of
approximately 1%, low overhead implementations of the entire Clifford group,
and flexible, arbitrarily long-range logical gates. These highly desirable
features come at the cost of significant classical processing complexity. We
show how to perform the processing associated with an nxn lattice of qubits,
each being manipulated in a realistic, fault-tolerant manner, in O(n^2) average
time per round of error correction. We also describe how to parallelize the
algorithm to achieve O(1) average processing per round, using only constant
computing resources per unit area and local communication. Both of these
complexities are optimal.Comment: 5 pages, 6 figures, published version with some additional tex
Vascular endothelial growth factor (VEGF) expression in locally advanced prostate cancer: secondary analysis of radiation therapy oncology group (RTOG) 8610.
BACKGROUND: Angiogenesis is a key element in solid-tumor growth, invasion, and metastasis. VEGF is among the most potent angiogenic factor thus far detected. The aim of the present study is to explore the potential of VEGF (also known as VEGF-A) as a prognostic and predictive biomarker among men with locally advanced prostate cancer.
METHODS: The analysis was performed using patients enrolled on RTOG 8610, a phase III randomized control trial of radiation therapy alone (Arm 1) versus short-term neoadjuvant and concurrent androgen deprivation and radiation therapy (Arm 2) in men with locally advanced prostate carcinoma. Tissue samples were obtained from the RTOG tissue repository. Hematoxylin and eosin slides were reviewed, and paraffin blocks were immunohistochemically stained for VEGF expression and graded by Intensity score (0-3). Cox or Fine and Gray\u27s proportional hazards models were used.
RESULTS: Sufficient pathologic material was available from 103 (23%) of the 456 analyzable patients enrolled in the RTOG 8610 study. There were no statistically significant differences in the pre-treatment characteristics between the patient groups with and without VEGF intensity data. Median follow-up for all surviving patients with VEGF intensity data is 12.2 years. Univariate and multivariate analyses demonstrated no statistically significant correlation between the intensity of VEGF expression and overall survival, distant metastasis, local progression, disease-free survival, or biochemical failure. VEGF expression was also not statistically significantly associated with any of the endpoints when analyzed by treatment arm.
CONCLUSIONS: This study revealed no statistically significant prognostic or predictive value of VEGF expression for locally advanced prostate cancer. This analysis is among one of the largest sample bases with long-term follow-up in a well-characterized patient population. There is an urgent need to establish multidisciplinary initiatives for coordinating further research in the area of human prostate cancer biomarkers
Electric Field-Tuned Topological Phase Transition in Ultra-Thin Na3Bi - Towards a Topological Transistor
The electric field induced quantum phase transition from topological to
conventional insulator has been proposed as the basis of a topological field
effect transistor [1-4]. In this scheme an electric field can switch 'on' the
ballistic flow of charge and spin along dissipationless edges of the
two-dimensional (2D) quantum spin Hall insulator [5-9], and when 'off' is a
conventional insulator with no conductive channels. Such as topological
transistor is promising for low-energy logic circuits [4], which would
necessitate electric field-switched materials with conventional and topological
bandgaps much greater than room temperature, significantly greater than
proposed to date [6-8]. Topological Dirac semimetals(TDS) are promising systems
in which to look for topological field-effect switching, as they lie at the
boundary between conventional and topological phases [3,10-16]. Here we use
scanning probe microscopy/spectroscopy (STM/STS) and angle-resolved
photoelectron spectroscopy (ARPES) to show that mono- and bilayer films of TDS
Na3Bi [3,17] are 2D topological insulators with bulk bandgaps >400 meV in the
absence of electric field. Upon application of electric field by doping with
potassium or by close approach of the STM tip, the bandgap can be completely
closed then re-opened with conventional gap greater than 100 meV. The large
bandgaps in both the conventional and quantum spin Hall phases, much greater
than the thermal energy kT = 25 meV at room temperature, suggest that ultrathin
Na3Bi is suitable for room temperature topological transistor operation
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