Analysis and Geometric Optimization of Single Electron Transistors for Read-Out in Solid-State Quantum Computing

The single electron transistor (SET) offers unparalled opportunities as a nano-scale electrometer, capable of measuring sub-electron charge variations. SETs have been proposed for read-out schema in solid-state quantum computing where quantum information processing outcomes depend on the location of a single electron on nearby quantum dots. In this paper we investigate various geometries of a SET in order to maximize the device's sensitivity to charge transfer between quantum dots. Through the use of finite element modeling we model the materials and geometries of an Al/Al2O3 SET measuring the state of quantum dots in the Si substrate beneath. The investigation is motivated by the quest to build a scalable quantum computer, though the methodology used is primarily that of circuit theory. As such we provide useful techniques for any electronic device operating at the classical/quantum interface.Comment: 13 pages, 17 figure

Brégand, Denise. -- Commerce caravanier et relations sociales au Bénin. Les Wangara du Borgou. Paris-Montréal, L'Harmattan, 1998, 272 p., cartes, bibl. (« Sociétés africaines et diaspora »).

The problem of definitively identifying the merchants of sub-Saharan West Africa who are collectively known as "Wangara" has engaged the interest of scholars from the times of the Arab chroniclers to modern historians like Nehemia Levtzion, Ivor Wilks, and Paul Lovejoy. The Wangara have long been identified with the early Muslim commercial networks of Ghana, Mali and their neighbors, and "Wangara" also came to signify corporate groupe controlling the external trace farther east in Song..

Synthesis and Cell Adhesive Properties of Linear and Cyclic RGD Functionalized Polynorbornene Thin Films

Described herein is the efficient synthesis and evaluation of bioactive arginine-glycine-aspartic acid (RGD) functionalized polynorbornene-based materials for cell adhesion and spreading. Polynorbornenes containing either linear or cyclic RGD peptides were synthesized by ring-opening metathesis polymerization (ROMP) using the well-defined ruthenium initiator [(H_(2)IMes)(pyr)_(2)(Cl)_(2)Ru═CHPh]. The random copolymerization of three separate norbornene monomers allowed for the incorporation of water-soluble polyethylene glycol (PEG) moieties, RGD cell recognition motifs, and primary amines for postpolymerization cross-linking. Following polymer synthesis, thin-film hydrogels were formed by cross-linking with bis(sulfosuccinimidyl) suberate (BS^3), and the ability of these materials to support human umbilical vein endothelial cell (HUVEC) adhesion and spreading was evaluated and quantified. When compared to control polymers containing either no peptide or a scrambled RDG peptide, polymers with linear or cyclic RGD at varying concentrations displayed excellent cell adhesive properties in both serum-supplemented and serum-free media. Polymers with cyclic RGD side chains maintained cell adhesion and exhibited comparable integrin binding at a 100-fold lower concentration than those carrying linear RGD peptides. The precise control of monomer incorporation enabled by ROMP allows for quantification of the impact of RGD structure and concentration on cell adhesion and spreading. The results presented here will serve to guide future efforts for the design of RGD functionalized materials with applications in surgery, tissue engineering, and regenerative medicine

A parking study for Central Square in Cambridge

Thesis (M.C.P.) Massachusetts Institute of Technology. Dept. of Architecture, 1950.Bibliography: leaves 100-102.by C. David Loeks.M.C.P

Quantitation of selective autophagic protein aggregate degradation in vitro and in vivo using luciferase reporters

The analysis of autophagy in cells and tissue has principally been performed via qualitative measures. These assays identify autophagosomes or measure the conversion of LC3I to LC3II. However, qualitative assays fail to quantitate the degradation of an autophagic substrate and therefore only indirectly measure an intact autophagic system. “Autophagic flux” can be measured using long-lived proteins that are degraded via autophagy. We developed a quantifiable luciferase reporter assay that measures the degradation of a long-lived polyglutamine protein aggregate, polyQ80-luciferase. Using this reporter, the induction of autophagy via starvation or rapamycin in cells preferentially decreases polyQ80-luciferase when compared with a non-aggregating polyQ19-luciferase after four hours of treatment. This response was both time- and concentration-dependent, prevented by autophagy inhibitors and absent in ATG5 knockout cells. We adapted this assay to living animals by electroporating polyQ19-luciferase and polyQ80-luciferase expression constructs into the right and left tibialis anterior (TA) muscles of mice, respectively. The change in the ratio of polyQ80-luciferase to polyQ19-luciferase signal before and after autophagic stimulation or inhibition was quantified via in vivo bioluminescent imaging. Following two days of starvation or treatment with intraperitoneal rapamycin, there was a ~35% reduction in the ratio of polyQ80:polyQ19-luciferase activity, consistent with the selective autophagic degradation of polyQ80 protein. This autophagic response in skeletal muscle in vivo was abrogated by co-treatment with chloroquine and in ATG16L1 hypomorphic mice. Our study demonstrates a method to quantify the autophagic flux of an expanded polyglutamine via luciferase reporters in vitro and in vivo

Coherent Tunneling Adiabatic Passage with the Alternating Coupling Scheme

The use of adiabatic passage techniques to mediate particle transport through real space, rather than phase space is becoming an interesting possibility. We have investigated the properties of Coherent Tunneling Adiabatic Passage (CTAP) with alternating tunneling matrix elements. This geometry, not previously considered in the donor in silicon paradigm, provides an interesting route to long-range quantum transport. We introduce simplified coupling protocols, and transient eigenspectra as well as a realistic gate design for this transport protocol. Using a pairwise treatment of the tunnel couplings for a 5 donor device with 30nm donor spacings, 120nm total chain length, we estimate the time scale required for adiabatic operation to be ~70ns, a time well within measured electron spin and estimated charge relaxation and times for phosphorus donors in silicon.Comment: 13 pages, 5 figures, minor revision

Ground Water in the Kentucky River Basin

Most private wells in the Kentucky River Basin are in unconfined or semi-confined bedrock aquifers. Within these aquifers, high-yield zones are irregularly distributed. The most productive wells are drilled into fractured bedrock and alluvium along the Kentucky River floodplain. The data indicate that ground water acts as a buffer to peak and low flows in Kentucky River Basin streams. At current withdrawal rates, ground-water usage does not seem to have an adverse impact on the Kentucky River. Privately owned ground-water sources supply approximately 135,000 people living in the basin-approximately 19 percent of the total population and 36 percent of the rural population. More than 50 percent of residential water supplies in eastern Kentucky rely on ground water. If aquifers are protected from pollution by wellhead protection programs and old wells are retrofitted to prevent direct contamination, then ground water will continue to provide a reliable water supply in many rural areas of the basin. However, for most of the basin, few wells will have yields adequate to supply a large demand. Ground water from present wells will not provide an adequate supply for communities with a population of over a few thousand. Limited discharge data available for springs and large wells in the basin strongly suggest that the potential for ground water to supplement current supplies should not be ignored. Discharge from well fields and springs could be used to augment surface supplies during drought. A better understanding of the distribution and quality of ground-water resources is crucial for the citizens of the basin to fully benefit from ground water

The Wide Brown Dwarf Binary Oph 1622-2405 and Discovery of A Wide, Low Mass Binary in Ophiuchus (Oph 1623-2402): A New Class of Young Evaporating Wide Binaries?

We imaged five objects near the star forming clouds of Ophiuchus with the Keck Laser Guide Star AO system. We resolved Allers et al. (2006)'s #11 (Oph 16222-2405) and #16 (Oph 16233-2402) into binary systems. The #11 object is resolved into a 243 AU binary, the widest known for a very low mass (VLM) binary. The binary nature of #11 was discovered first by Allers (2005) and independently here during which we obtained the first spatially resolved R~2000 near-infrared (J & K) spectra, mid-IR photometry, and orbital motion estimates. We estimate for 11A and 11B gravities (log(g)>3.75), ages (5+/-2 Myr), luminosities (log(L/Lsun)=-2.77+/-0.10 and -2.96+/-0.10), and temperatures (Teff=2375+/-175 and 2175+/-175 K). We find self-consistent DUSTY evolutionary model (Chabrier et al. 2000) masses of 17+4-5 MJup and 14+6-5 MJup, for 11A and 11B respectively. Our masses are higher than those previously reported (13-15 MJup and 7-8 MJup) by Jayawardhana & Ivanov (2006b). Hence, we find the system is unlikely a ``planetary mass binary'', (in agreement with Luhman et al. 2007) but it has the second lowest mass and lowest binding energy of any known binary. Oph #11 and Oph #16 belong to a newly recognized population of wide (>100 AU), young (<10 Myr), roughly equal mass, VLM stellar and brown dwarf binaries. We deduce that ~6+/-3% of young (<10 Myr) VLM objects are in such wide systems. However, only 0.3+/-0.1% of old field VLM objects are found in such wide systems. Thus, young, wide, VLM binary populations may be evaporating, due to stellar encounters in their natal clusters, leading to a field population depleted in wide VLM systems.Comment: Accepted version V2. Now 13 pages longer (45 total) due to a new discussion of the stability of the wide brown dwarf binary population, new summary Figure 17 now included, Astrophysical Journal 2007 in pres

Durability of open repair of juxtarenal abdominal aortic aneurysms

ObjectiveAs branched/fenestrated endografts expand endovascular options for juxtarenal abdominal aortic aneurysms (JAAAs), long-term durability will be compared to that of open JAAA repair, which has not been documented in large contemporary series. The goal of this study was to assess the late clinical and anatomic outcomes after open JAAA repair.MethodsFrom July 2001 to December 2007, 199 patients underwent open elective JAAA repair, as defined by a need for suprarenal clamping. End points included perioperative and late survival, long-term follow-up of renal function, and freedom from graft-related complications. Factors predictive of survival were determined by multivariate analysis.ResultsThe mean patient age was 74 years, 71% were men, and 20% had baseline renal insufficiency (Cr >1.5). Thirty-seven renal artery bypasses, for anatomic necessity or ostial stenosis, were performed in 36 patients. Overall 30-day mortality was 2.5%. Four patients (2.0%) required early dialysis; one patient recovered by discharge. Two additional patients progressed to dialysis over long-term follow-up. There was one graft infection involving one limb of a bifurcated graft. Surveillance imaging was obtained in 101 patients (72% of survivors) at a mean follow-up of 41 ± 28 months. Renal artery occlusion occurred in four patients (3% of imaged renal arteries; one native/three grafts). Two patients (2.0%) had aneurysmal degeneration of the aorta either proximal or distal to the repaired segment, but there were no anastomotic pseudoaneurysms. Remote aneurysms were found in 29 patients (29% of imaged patients), 14 of whom had descending thoracic aneurysm or TAAA. Four patients underwent subsequent thoracic endovascular aneurysm repair (TEVAR). Actuarial survival was 74 ± 3.3% at 5 years. Negative predictors of survival included increasing age at the time of operation (relative risk [RR], 1.05; P = .01), steroid use (RR, 2.20; P = .001), and elevated preoperative creatinine (RR, 1.73; P = .02).ConclusionsOpen JAAA repair yields excellent long-term anatomic durability and preserves renal function. Perioperative renal insufficiency occurs in 8.5% of patients, but few of them progress to dialysis. Graft-related complications are rare (2% at 40 months); however, axial imaging revealed descending thoracic aneurysms in 14% of imaged patients, making continued surveillance for remote aneurysms prudent. These data provide a benchmark against which fenestrated/branched endovascular aneurysm repair (EVAR) outcomes can be compared