Quantum transport in carbon nanotubes

Carbon nanotubes are a versatile material in which many aspects of condensed matter physics come together. Recent discoveries, enabled by sophisticated fabrication, have uncovered new phenomena that completely change our understanding of transport in these devices, especially the role of the spin and valley degrees of freedom. This review describes the modern understanding of transport through nanotube devices. Unlike conventional semiconductors, electrons in nanotubes have two angular momentum quantum numbers, arising from spin and from valley freedom. We focus on the interplay between the two. In single quantum dots defined in short lengths of nanotube, the energy levels associated with each degree of freedom, and the spin-orbit coupling between them, are revealed by Coulomb blockade spectroscopy. In double quantum dots, the combination of quantum numbers modifies the selection rules of Pauli blockade. This can be exploited to read out spin and valley qubits, and to measure the decay of these states through coupling to nuclear spins and phonons. A second unique property of carbon nanotubes is that the combination of valley freedom and electron-electron interactions in one dimension strongly modifies their transport behaviour. Interaction between electrons inside and outside a quantum dot is manifested in SU(4) Kondo behavior and level renormalization. Interaction within a dot leads to Wigner molecules and more complex correlated states. This review takes an experimental perspective informed by recent advances in theory. As well as the well-understood overall picture, we also state clearly open questions for the field. These advances position nanotubes as a leading system for the study of spin and valley physics in one dimension where electronic disorder and hyperfine interaction can both be reduced to a very low level.Comment: In press at Reviews of Modern Physics. 68 pages, 55 figure

Estimation in sera by radioimmunoassay of a specific membrane antigen associated with a murine lymphoma.

Material with a molecular weight of less than 10(5) daltons has been isolated and partially purified from the ascitic fluid of DBA2 mice bearing a syngeneic lymphoma (SL2). This substance inhibits the cytotoxic action of an allogeneic antiserum directed specifically against SL2 cells. Material has been rendered radioactive with 125I and between 20 and 25% of the radioactivity is bound in a specific manner to the antiserum. The material which is referred to as 125I-TSTA has been used in a radioimmunoassay to measure the level of TSTA in the sera of mice bearing both ascitic and subcutaneous SL2 tumours. The level of circulating TSTA was found to be high immediatley following inoculation of live SL2 cells, probably because a large proportion of the injected cells autolyse. The serum concentration of TSTA then falls but 6-10 days later begins to rise again in parallel with the growth of the SL2 tumour either in the peritoneal cavity or subcutaneously. Following surgical removal of an intradermal SL2 tumour the level of TSTA in the serum falls rapidly. No evidence could be found that a significant proportion of the TSTA in the serum of tumour-bearing mice is completed with antibody. However, in the serum of DBA2 mice which have been hyperimmunized with irradiated SL2 cells there are antibodies which bind 125I-TSTA although syngeneic anti-SL2 sera, unlike alloantisera, do not show complement dependent lysis of SL2 cells

Extended Water Quality Monitoring of the Lincoln Lake Watershed

For seven years, the Lincoln Lake (Moores Creek and Beatty Branch) watershed was monitored for improvements in water quality resulting from agricultural best management practices (BMP) implemented to reduce nutrient transport. During the first three years of monitoring (1991 to 1994), nitrogen transport declined significantly (Edwards et al., 1994, 1996, and 1997) under both base and storm flow conditions. This decline in nitrogen transport was again observed in the three-year period following 1994 (Vendrell et al. 1998). This monitoring effort has demonstrated that water quality bas improved in the Lincoln Lake watershed. However, since the nitrogen transport continued to decline and there was some indication that phosphorus may begin to decline, monitoring was extended for another year (1998)

Imaging Transport Resonances in the Quantum Hall Effect

We use a scanning capacitance probe to image transport in the quantum Hall system. Applying a DC bias voltage to the tip induces a ring-shaped incompressible strip (IS) in the 2D electron system (2DES) that moves with the tip. At certain tip positions, short-range disorder in the 2DES creates a quantum dot island in the IS. These islands enable resonant tunneling across the IS, enhancing its conductance by more than four orders of magnitude. The images provide a quantitative measure of disorder and suggest resonant tunneling as the primary mechanism for transport across ISs.Comment: 4 pages, 4 figures, submitted to PRL. For movies and additional infomation, see http://electron.mit.edu/scanning/; Added scale bars to images, revised discussion of figure 3, other minor change

Variation between European eel Anguilla anguilla (L.) stocks in five marshes of the Thames Estuary (United Kingdom)

The European eel (Anguilla anguilla, L.) was historically widely distributed throughout the United Kingdom, in coastal waters, lakes, rivers and wetlands. Recruitment has declined in recent decades and the species is now listed as ‘Critically Endangered’ on the International Union for Conservation of Nature and Natural Resources (IUCN) Red List. Management of suitable wetland habitats may contribute to species recovery; however, little is known about the stocks in these areas. In this study, yellow (adult stage > 300 mm) eels were sampled in ditches in five marshes bordering the Thames Estuary in England, UK. Ecological variables, including ditch characteristics, invertebrate abundance and water quality parameters were measured. Habitat features were also observed and recorded, including access, land use and water management regimes. Eels were found in all marshes, but at varying catch-per-unit-effort (CPUE). There were no significant correlations between CPUE and the ecological variables, except ditch width. However, a significant difference in CPUE was found between two of the marshes, which may be explained by variations in local habitat management. Mean lengths showed a high proportion of females and mean body condition of four of the marshes was also found to be greater than in three rivers in the same region. These findings suggest that the marshes are potentially favourable eel habitats and that factors influencing habitat quality, such as land use and water management, may affect eel abundance, production of females and body condition. Effective management of such wetlands may therefore contribute to the conservation of European eel

Student Ensemble: Symphonic Band and Symphonic Winds

Center for the Performing ArtsOctober 9, 2011Sunday Afternoon3:00 p.m

Symphonic Band Symphonic Winds

Center for the Performing Arts Sunday Afternoon September 30, 2007 3:00p.m

Technologies for Future High Capability Micro-Milsatcom Systems

Satellite communications systems are a vitally important component of our Defense infrastructure for both tactical and strategic missions. In particular, satellite communications (whether military or commercial) have become increasingly important to support tactical operations, as was clearly demonstrated during Operations Desert Shield and Desert Storm. In the emerging doctrinal shift to a CONUS-based force structure with capabilities for rapidly responsive lethal power projection to meet global crises, the vital necessity for SATCOM to provide an omnipresent communications infrastructure for immediate support of the developing theater will become a key element in the successful realization of our new warfighting strategy. This infrastructure must provide RF bandwidth on demand and access to ATM switches and B-ISDN or SONET services as required from any worldwide location for any type of terminal. DARPA is developing the enabling technologies to give future systems the ability to realize their potential for becoming more affordable, more capable and more accessible by a theater commander. Advanced technologies are facilitating microminiaturization of key subsystems for communications satellite payloads, their host satellite buses, terminals and interfaces with terrestrial systems. These technologies can enhance the capability density of large spacecraft, as well as facilitate small, highly capable space and terrestrial assets, which can be labeled microMILSATCOM systems