Transport in coupled graphene-nanotube quantum devices

We report on the fabrication and characterization of all-carbon hybrid quantum devices based on graphene and single-walled carbon nanotubes. We discuss both, carbon nanotube quantum dot devices with graphene charge detectors and nanotube quantum dots with graphene leads. The devices are fabricated by chemical vapor deposition growth of carbon nanotubes and subsequent structuring of mechanically exfoliated graphene. We study the detection of individual charging events in the carbon nanotube quantum dot by a nearby graphene nanoribbon and show that they lead to changes of up to 20% of the conductance maxima in the graphene nanoribbon acting as a good performing charge detector. Moreover, we discuss an electrically coupled graphene-nanotube junction, which exhibits a tunneling barrier with tunneling rates in the low GHz regime. This allows to observe Coulomb blockade on a carbon nanotube quantum dot with graphene source and drain leads

Solution of the Complex Action Problem in the Potts Model for Dense QCD

Monte Carlo simulations of lattice QCD at non-zero baryon chemical potential $\mu$ suffer from the notorious complex action problem. We consider QCD with static quarks coupled to a large chemical potential. This leaves us with an SU(3) Yang-Mills theory with a complex action containing the Polyakov loop. Close to the deconfinement phase transition the qualitative features of this theory, in particular its Z(3) symmetry properties, are captured by the 3-d 3-state Potts model. We solve the complex action problem in the Potts model by using a cluster algorithm. The improved estimator for the $\mu$-dependent part of the Boltzmann factor is real and positive and is used for importance sampling. We localize the critical endpoint of the first order deconfinement phase transition line and find consistency with universal 3-d Ising behavior. We also calculate the static quark-quark, quark-anti-quark, and anti-quark-anti-quark potentials which show screening as expected for a system with non-zero baryon density.Comment: 28 pages, 7 figure

Adjoint Wilson Line in SU(2) Lattice Gauge Theory

The behavior of the adjoint Wilson line in finite-temperature, $SU(2)$, lattice gauge theory is discussed. The expectation value of the line and the associated excess free energy reveal the response of the finite-temperature gauge field to the presence of an adjoint source. The value of the adjoint line at the critical point of the deconfining phase transition is highlighted. This is not calculable in weak or strong coupling. It receives contributions from all scales and is nonanalytic at the critical point. We determine the general form of the free energy. It includes a linearly divergent term that is perturbative in the bare coupling and a finite, nonperturbative piece. We use a simple flux tube model to estimate the value of the nonperturbative piece. This provides the normalization needed to estimate the behavior of the line as one moves along the critical curve into the weak coupling region.Comment: 21 pages, no figures, Latex/Revtex 3, UCD-93-1

Z2 Monopoles, Vortices, and the Deconfinement Transition in Mixed Action SU(2) Gauge Theory

Adding separate chemical potentials lambda and gamma for Z2 monopoles and vortices respectively in the Villain form of the mixed fundamental-adjoint action for the SU(2) lattice gauge theory, we investigate their role in the interplay between the deconfinement and bulk phase transitions using Monte Carlo techniques. Setting lambda to be nonzero, we find that the line of deconfinement transitions is shifted in the coupling plane but it behaves curiously also like the bulk transition line for large enough adjoint coupling, as for lambda=0. In a narrow range of couplings, however, we find separate deconfinement and bulk phase transitions on the same lattice for nonzero and large lambda, suggesting the two to be indeed coincident in the region where a first order deconfinement phase transition is seen. In the limit of large lambda and gamma, we obtain only lines of second order deconfinement phase transitions, as expected from universality.Comment: 18 pages, 10 figures include

Photodynamic therapy using intravenous delta-aminolaevulinic acid-induced protoporphyrin IX sensitisation in experimental hepatic tumours in rats.

The efficacy of photodynamic therapy (PDT) using delta-aminolaevulinic acid (ALA)-induced protoporphyrin IX (PpIX) sensitisation and laser light at 635 nm was investigated in the treatment of experimental hepatic tumours. The model of liver tumours was induced either by local inoculation or by administration of tumour cells through the portal vein in rats. ALA at a dose of 60 mg kg(-1) b.w. was intravenously administered 60 min before PDT. PpIX accumulation in tumour, normal liver and abdominal wall muscle was detected by means of laser-induced fluorescence (LIF). Laser Doppler imaging (LDI) was used to determine changes in the superficial blood flow in connection with PDT. Histopathological examinations were performed to evaluate the PDT effects on the tumour and the surrounding liver tissue, including pathological features in the microvascular system. The accumulation of PpIX, as monitored by LIF, showed high fluorescence intensities at about 635 nm in both the hepatic tumour tissue and normal liver and low values in the abdominal wall. LDI demonstrated that the blood flow in the treated tumour and its surrounding normal liver tissue decreased immediately after the PDT, indicating an effect on the vascular system. A large number of thrombi in the irradiated tumour were found microscopically 3 h after the PDT. The tumour growth rate showed a marked decrease when evaluated 3 and 6 days after the treatment. These results show that the ALA-PDT is effective in the inhibition of growth of experimental hepatic tumours

Rapidly rotating Bose-Einstein condensates in anharmonic potentials

Rapidly rotating Bose-Einstein condensates confined in anharmonic traps can exhibit a rich variety of vortex phases, including a vortex lattice, a vortex lattice with a hole, and a giant vortex. Using an augmented Thomas-Fermi variational approach to determine the ground state of the condensate in the rotating frame -- valid for sufficiently strongly interacting condensates -- we determine the transitions between these three phases for a quadratic-plus-quartic confining potential. Combining the present results with previous numerical simulations of small rotating condensates in such anharmonic potentials, we delineate the general structure of the zero temperature phase diagram.Comment: 5 pages, 5 figure

The Thermodynamics of Quarks and Gluons

This is an introduction to the study of strongly interacting matter. We survey its different possible states and discuss the transition from hadronic matter to a plasma of deconfined quarks and gluons. Following this, we summarize the results provided by lattice QCD finite temperature and density, and then investigate the nature of the deconfinement transition. Finally we give a schematic overview of possible ways to study the properties of the quark-gluon plasma.Comment: 19 pages, 21 figures; lecture given at the QGP Winter School, Jaipur/India, Feb.1-3, 2008; to appear in Springer Lecture Notes in Physic

Magnetic and Thermodynamic Stability of SU(2) Yang-Mills Theory

SU(2) Yang-Mills theory at finite extension or, equivalently, at finite temperature is probed by a homogeneous chromomagnetic field. We use a recent modified axial gauge formulation which has the novel feature of respecting the center symmetry in perturbation theory. The characteristic properties of the Z_2-symmetric phase, an extension-dependent mass term and antiperiodic boundary conditions, provide stabilization against magnetic field formation for sufficiently small extension or high temperature. In an extension of this investigation to the deconfined phase with broken center symmetry, the combined constraints of thermodynamic and magnetic stability are shown to yield many of the high temperature properties of lattice SU(2) gauge theory.Comment: 27 pages, LATEX, 7 postscript figures, corrected typo

The Hamburg/SAO Survey for Emission-Line Galaxies. III. The Third List of 81 Galaxies

We present the third list with results {Tables 2 to 6 are available only in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html. Figures A1 to A9 will be made available only in the electronic version of the journal.} of the Hamburg/SAO Survey for Emission-Line Galaxies (HSS therein, SAO - Special Astrophysical Observatory, Russia). This survey is based on the digitized objective-prism photoplate database of the Hamburg Quasar Survey (HQS). Here, we present new spectroscopic results of candidates which were obtained in 1998 with the 2.1 m KPNO and the 2.2 m Calar Alto telescopes. All candidates are selected in the declination band +35$^{\circ}$ to +40$^{\circ}$. The follow-up spectroscopy with the 2 m class telescopes confirmed 85 emission-line objects out of 113 observed candidates and allowed their quantitative spectral classification. For 80 of them, the redshifts are determined for the first time. For 5 previously known ELGs, line ratios are presented for the first time. We could classify 55 out of the 85 emission-line objects as BCG/H{\sc ii} galaxies or probable BCGs, 4 - as QSOs, 6 - as Seyfert galaxies, 1 - as super-association in a subluminous spiral galaxy, and 11 are low-excitation objects - either starburst nuclear (SBN), or dwarf amorphous nuclear starburst galaxies (DANS). We could not classify 8 ELGs. Further, for 8 more galaxies we did not detect any significant emission lines.Comment: A&A latex file with 8 tables and one figure. Astron. Astrophys. Suppl. accepted 200