Quantum Computer Using Coupled Quantum Dot Molecules

We propose a method for implementation of a quantum computer using artificial molecules. The artificial molecule consists of two coupled quantum dots stacked along z direction and one single electron. One-qubit and two-qubit gates are constructed by one molecule and two coupled molecules, respectively.The ground state and the first excited state of the molecule are used to encode the |0> and |1> states of a qubit. The qubit is manipulated by a resonant electromagnetic wave that is applied directly to the qubit through a microstrip line. The coupling between two qubits in a quantum controlled NOT gate is switched on (off) by floating (grounding) the metal film electrodes. We study the operations of the gates by using a box-shaped quantum dot model and numerically solving a time-dependent Schridinger equation, and demonstrate that the quantum gates can perform the quantum computation. The operating speed of the gates is about one operation per 4ps. The reading operation of the output of the quantum computer can be performed by detecting the polarization of the qubits.Comment: 18 pages, 7 figures, submitted to Jpn. J. Appl. Phys, please send your e-mail to Nan-Jian Wu <[email protected]

c-Myc induced changes in higher order rDNA structure accompany growth factor stimulation of quiescent cells

Human c-Myc is believed to be a high level coordinator of protein synthesis capacity and cell growth rate, capable of activating transcription by all three nuclear RNA Polymerases. Direct activation of rDNA transcription by c-Myc is functionally conserved in rat cells, despite high divergence in non-coding rDNA sequences, suggesting that this coordinating role is likely to be a general within mammals. Upon re-feeding of starved cells, c-Myc activity enhances the efficiency of RNA Polymerase I and SL1/TIF-1B recruitment to the rDNA and rapidly induces higher order gene loop structures in rDNA chromatin that juxtapose upstream and downstream rDNA sequences. Furthermore c-Myc induced gene-loop formation in rDNA genes occurs independently of rDNA transcription, implying that it may be an early step in the re-programming of quiescent cells as they enter the growth cycle

RRR: Rank-Regret Representative

Selecting the best items in a dataset is a common task in data exploration. However, the concept of "best" lies in the eyes of the beholder: different users may consider different attributes more important, and hence arrive at different rankings. Nevertheless, one can remove "dominated" items and create a "representative" subset of the data set, comprising the "best items" in it. A Pareto-optimal representative is guaranteed to contain the best item of each possible ranking, but it can be almost as big as the full data. Representative can be found if we relax the requirement to include the best item for every possible user, and instead just limit the users' "regret". Existing work defines regret as the loss in score by limiting consideration to the representative instead of the full data set, for any chosen ranking function. However, the score is often not a meaningful number and users may not understand its absolute value. Sometimes small ranges in score can include large fractions of the data set. In contrast, users do understand the notion of rank ordering. Therefore, alternatively, we consider the position of the items in the ranked list for defining the regret and propose the {\em rank-regret representative} as the minimal subset of the data containing at least one of the top-$k$ of any possible ranking function. This problem is NP-complete. We use the geometric interpretation of items to bound their ranks on ranges of functions and to utilize combinatorial geometry notions for developing effective and efficient approximation algorithms for the problem. Experiments on real datasets demonstrate that we can efficiently find small subsets with small rank-regrets

Evaluation of cover materials for a large scale test facility at Key Lake

Engineered soil cover systems have gained popularity in recent years as a preferred method of decommissioning and reclaiming waste management facilities. The main functions of a soil cover system are to minimize water infiltration, limit gas migration, resist weathering and erosion, and provide support for vegetation. In 1992, Cameco Corporation constructed a large scale non-vegetated prototype soil cover at Key Lake in north-central Saskatchewan. Their main objective was to evaluate the suitability of using local tills and sands for cover materials during future decommissioning of various waste management facilities at the site. An instrumentation and monitoring program was initiated in 1993 to verify the field performance of the soil cover system. The prototype soil cover was constructed over leached cobble ore that was enclosed within a double lined containment system. The soil cover consisted of a 60 cm layer of outwash glacial sand overlain by a 60 cm layer of compacted till. The test facility is essentially a large scale lysimeter whereby net infiltration is determined by monitoring the change in water table depth, the quantity of water removed from the facility, and the soil moisture profile. The instrumentation and monitoring program included a weather station, thermal conductivity sensors and neutron probe access holes, a Bowen Ratio Instrumentation, and a runoff collection and monitoring system. A laboratory program was undertaken to define pertinent soil parameters such as the soil-water characteristic curve and hydraulic conductivity. Laboratory calibration of the neutron probe was also carried out. A field soil testing program was completed to determine in situ density and hydraulic conductivity. The weather monitoring program yielded reliable precipitation, air temperature, and wind speed data. Instrumentation error was noted for relative humidity, net radiation, and pan evaporation parameters. The surface runoff monitoring system provided reliable runoff data on a real time basis. The thermal conductivity sensors were found to underestimate the soil moisture content, while the neutron probe was found to overestimate. The laboratory testing indicated that the outwash sand and the compacted till possessed similar soil water characteristic curves. The similarities in their water storage and release characteristics preclude the ability of these soils to form an effective capillary barrier when the till is overlain by the outwash sand. The field investigation has revealed that the soil cover system was underlain by a layer of extraneous sand and till material, most likely used to grade the facility prior to constructing the soil cover. The field performance of an engineered soil cover system is determined by the net infiltration through the system. The net infiltration for the 1996-1997 monitoring year was estimated to be 52% (287 mm) of the total annual precipitation(555 mm of precipitation from October 1996 to April 1997, inclusively). There was an insignificant change in the subsurface soil moisture storage. The surface runoff was recorded to be 6% (35 mm) of the total annual precipitation. The actual evaporation was estimated to be 30% (167 mm). The evaluation of the soil cover design has suggested that the Key Lake outwash sand overlain by the Key Lake till will not form a capillary barrier. Furthermore, the thickness of the till layer far exceeded the evaporative zone depth of the material, and therefore, infiltrated water could not have been extracted through evaporation even if the two soils had formed a capillary barrier. The net water storage capacity of the cover system was found to be inadequate (12 mm) to store larger rainfall events, thus further contributing to net infiltration. Incorporating surface vegetation has the potential to increase the total storage capacity to 42 mm; vegetation will also increase total evapotranspiration. A detailed analysis of the surface runoff and infiltration characteristics has indicated that runoff was governed by rainfall intensity and antecedent soil moisture conditions. Surface runoff was generated regardless of soil moisture conditions when the 15-minute rainfall intensity exceeded 1.4 mm. This intensity corresponds to a surface hydraulic conductivity (till) of 1.5 x 10-6 m/s; the laboratory determined hydraulic conductivity was 2.0 x 10-7 m/s

Thermal Bremsstrahlung Radiation in a Two-Temperature Plasma

In the normal one-temperature plasma the motion of ions is usually neglected when calculating the Bremsstrahlung radiation of the plasma. Here we calculate the Bremsstrahlung radiation of a two-temperature plasma by taking into account of the motion of ions. Our results show that the total radiation power is always lower if the motion of ions is considered. We also apply the two-temperature Bremsstrahlung radiation mechanism for an analytical Advection-Dominated Accretion Flow (ADAF) model; we find the two-temperature correction to the total Bremsstrahlung radiation for ADAF is negligible.Comment: 5 pages, 4 figures, accepted for publication in CHJAA. Some discussions and references adde

Faddeev calculation of pentaquark Θ+\Theta^+ in the Nambu-Jona-Lasinio model-based diquark picture

A Bethe-Salpeter-Faddeev (BSF) calculation is performed for the pentaquark $\Theta^+$ in the diquark picture of Jaffe and Wilczek in which $\Theta^+$ is a diquark-diquark-${\bar s}$ three-body system. Nambu-Jona-Lasinio (NJL) model is used to calculate the lowest order diagrams in the two-body scatterings of ${\bar s}D$ and $D D$. With the use of coupling constants determined from the meson sector, we find that ${\bar s}D$ interaction is attractive in s-wave while $DD$ interaction is repulsive in p-wave. With only the lowest three-body channel considered, we do not find a bound $\frac 12^+$ pentaquark state. Instead, a bound pentaquark $\Theta^+$ with $\frac 12^-$ is obtained with a unphysically strong vector mesonic coupling constants.Comment: 22 pages, 11 figures, accepted version in Phys. Rev. C. Summary of main changes/corrections: 1. "which only holds at tree level" below the eq. (23) is added. 2. In the last paragraph of p.23 we added a remark that the coupling constant obtained from Lambda mass is different from the estimate as obtained from the meson spectru