One-dimensional conduction in Charge-Density Wave nanowires

We report a systematic study of the transport properties of coupled one-dimensional metallic chains as a function of the number of parallel chains. When the number of parallel chains is less than 2000, the transport properties show power-law behavior on temperature and voltage, characteristic for one-dimensional systems.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let

Unstable magnetohydrodynamical continuous spectrum of accretion disks. A new route to magnetohydrodynamical turbulence in accretion disks

We present a detailed study of localised magnetohydrodynamical (MHD) instabilities occuring in two--dimensional magnetized accretion disks. We model axisymmetric MHD disk tori, and solve the equations governing a two--dimensional magnetized accretion disk equilibrium and linear wave modes about this equilibrium. We show the existence of novel MHD instabilities in these two--dimensional equilibria which do not occur in an accretion disk in the cylindrical limit. The disk equilibria are numerically computed by the FINESSE code. The stability of accretion disks is investigated analytically as well as numerically. We use the PHOENIX code to compute all the waves and instabilities accessible to the computed disk equilibrium. We concentrate on strongly magnetized disks and sub--Keplerian rotation in a large part of the disk. These disk equilibria show that the thermal pressure of the disk can only decrease outwards if there is a strong gravitational potential. Our theoretical stability analysis shows that convective continuum instabilities can only appear if the density contours coincide with the poloidal magnetic flux contours. Our numerical results confirm and complement this theoretical analysis. Furthermore, these results show that the influence of gravity can either be stabilizing or destabilizing on this new kind of MHD instability. In the likely case of a non--constant density, the height of the disk should exceed a threshold before this type of instability can play a role. This localised MHD instability provides an ideal, linear route to MHD turbulence in strongly magnetized accretion disk tori.Comment: 20 pages, 10 figures, accepted for publication in Astronomy & Astrophysic

Toward detailed prominence seismology - I. Computing accurate 2.5D magnetohydrodynamic equilibria

Context. Prominence seismology exploits our knowledge of the linear eigenoscillations for representative magnetohydro- dynamic models of filaments. To date, highly idealized models for prominences have been used, especially with respect to the overall magnetic configurations. Aims. We initiate a more systematic survey of filament wave modes, where we consider full multi-dimensional models with twisted magnetic fields representative of the surrounding magnetic flux rope. This requires the ability to compute accurate 2.5 dimensional magnetohydrodynamic equilibria that balance Lorentz forces, gravity, and pressure gradients, while containing density enhancements (static or in motion). Methods. The governing extended Grad-Shafranov equation is discussed, along with an analytic prediction for circular flux ropes for the Shafranov shift of the central magnetic axis due to gravity. Numerical equilibria are computed with a finite element-based code, demonstrating fourth order accuracy on an explicitly known, non-trivial test case. Results. The code is then used to construct more realistic prominence equilibria, for all three possible choices of a free flux-function. We quantify the influence of gravity, and generate cool condensations in hot cavities, as well as multi- layered prominences. Conclusions. The internal flux rope equilibria computed here have the prerequisite numerical accuracy to allow a yet more advanced analysis of the complete spectrum of linear magnetohydrodynamic perturbations, as will be demonstrated in the companion paper.Comment: Accepted by Astronomy & Astrophysics, 15 pages, 15 figure

Toward detailed prominence seismology - II. Charting the continuous magnetohydrodynamic spectrum

Starting from accurate MHD flux rope equilibria containing prominence condensations, we initiate a systematic survey of their linear eigenoscillations. To quantify the full spectrum of linear MHD eigenmodes, we require knowledge of all flux-surface localized modes, charting out the continuous parts of the MHD spectrum. We combine analytical and numerical findings for the continuous spectrum for realistic prominence configurations. The equations governing all eigenmodes for translationally symmetric, gravitating equilibria containing an axial shear flow, are analyzed, along with their flux-surface localized limit. The analysis is valid for general 2.5D equilibria, where either density, entropy, or temperature vary from one flux surface to another. We analyze the mode couplings caused by the poloidal variation in the flux rope equilibria, by performing a small gravity parameter expansion. We contrast the analytical results with continuous spectra obtained numerically. For equilibria where the density is a flux function, we show that continuum modes can be overstable, and we present the stability criterion for these convective continuum instabilities. Furthermore, for all equilibria, a four-mode coupling scheme between an Alfvenic mode of poloidal mode number m and three neighboring (m-1, m, m+1) slow modes is identified, occurring in the vicinity of rational flux surfaces. For realistically prominence equilibria, this coupling is shown to play an important role, from weak to stronger gravity parameter g values. The analytic predictions for small g are compared with numerical spectra, and progressive deviations for larger g are identified. The unstable continuum modes could be relevant for short-lived prominence configurations. The gaps created by poloidal mode coupling in the continuous spectrum need further analysis, as they form preferred frequency ranges for global eigenoscillations.Comment: Accepted by Astronmy & Astrophysics, 21 pages, 15 figure

Charge Transport Processes in a Superconducting Single-Electron Transistor Coupled to a Microstrip Transmission Line

We have investigated charge transport processes in a superconducting single-electron transistor (S-SET) fabricated in close proximity to a two-dimensional electron gas (2DEG) in a GaAs/AlGaAs heterostructure. The macroscopic bonding pads of the S-SET along with the 2DEG form a microstrip transmission line. We observe a variety of current-carrying cycles in the S-SET which we attribute to simultaneous tunneling of Cooper pairs and emission of photons into the microstrip. We find good agreement between these experimental results and simulations including both photon emission and photon-assisted tunneling due to the electromagnetic environment.Comment: 4 pages, 4 figures, REVTeX

Behavioural addiction-A rising tide?

The term 'addiction' was traditionally used in relation to centrally active substances, such as cocaine, alcohol, or nicotine. Addiction is not a unitary construct but rather incorporates a number of features, such as repetitive engagement in behaviours that are rewarding (at least initially), loss of control (spiralling engagement over time), persistence despite untoward functional consequences, and physical dependence (evidenced by withdrawal symptoms when intake of the substance diminishes). It has been suggested that certain psychiatric disorders characterized by maladaptive, repetitive behaviours share parallels with substance addiction and therefore represent 'behavioural addictions'. This perspective has influenced the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), which now has a category 'Substance Related and Addictive Disorders', including gambling disorder. Could other disorders characterised by repetitive behaviours, besides gambling disorder, also be considered 'addictions'? Potential examples include kleptomania, compulsive sexual behaviour, 'Internet addiction', trichotillomania (hair pulling disorder), and skin-picking disorder. This paper seeks to define what is meant by 'behavioural addiction', and critically considers the evidence for and against this conceptualisation in respect of the above conditions, from perspectives of aetiology, phenomenology, co-morbidity, neurobiology, and treatment. Research in this area has important implications for future diagnostic classification systems, neurobiological models, and novel treatment directions.This research was supported by a Grant from the Academy of Medical Sciences (UK) to Dr Chamberlain. Dr Chamberlain consults for Cambridge Cognition. Dr Grant has received research Grants from the National Center for Responsible Gaming, and Forest and Roche Pharmaceuticals. Dr Grant receives yearly compensation from Springer Publishing for acting as Editor-in-Chief of the Journal of Gambling Studies and has received royalties from Oxford University Press, American Psychiatric Publishing, Inc., Norton Press, and McGraw Hill. Dr. Goudriaan was supported by an innovative scheme Grant of the Dutch Scientific Association (ZonMw VIDI Grant no. 016.136.354) and received support from the European Association for Alcohol Research, the National Center for Responsible Gaming and has consulted for TüV Germany. The other authors report no potential conflicts of interest or funding declarationsThis is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.euroneuro.2015.08.01

Temporary diverting stoma in therapy-refractory luminal colonic Crohn's disease:an alternative to immediate colorectal resection?

AimCreation of a diverting stoma in patients with Crohn's disease (CD) can counteract luminal inflammation. The clinical utility of a diverting stoma with the prospect of restoration of gastrointestinal continuity warrants further investigation. The aim of this work was to evaluate the long-term effects of creation of a diverting stoma on the disease course in patients with luminal colonic CD.MethodIn this retrospective, multicentre cohort study we investigated the disease course of patients who received a diverting stoma in the biological era. Clinical characteristics, medication use and surgical course were assessed at the time of creation of the diverting stoma and during follow-up. The primary outcome was the rate of successful and lasting reestablishment of gastrointestinal continuity.ResultsThirty six patients with refractory luminal CD from four institutions underwent creation of a diverting stoma. Of the overall cohort, 20 (56%) patients had their gastrointestinal continuity reestablished after initial stoma creation and 14 (39%) who had their stoma reversed remained stoma-free during a median of 3.3 years follow-up (interquartile range 2.1–6.1 years). Absence of stoma reversal was associated with the presence of proctitis (p = 0.02). Colorectal resection after creation of a diverting stoma was performed in 28 (78%) patients, with 7 (19%) having a less extensive resection and 6 (17%) having a more extensive resection compared with the surgical plan before stoma creation.ConclusionA diverting stoma could potentially be an alternative to immediate definitive stoma placement in specific populations consisting of patients with luminal colonic CD, especially in the absence of proctitis

The (co-)occurrence of problematic video gaming, substance use, and psychosocial problems in adolescents

Aims. The current study explored the nature of problematic (addictive) video gaming and the association with game type, psychosocial health, and substance use. Methods. Data were collected using a paper and pencil survey in the classroom setting. Three samples were aggregated to achieve a total sample of 8478 unique adolescents. Scales included measures of game use, game type, the Video game Addiction Test (VAT), depressive mood, negative self-esteem, loneliness, social anxiety, education performance, and use of cannabis, alcohol and nicotine (smoking). Results. Findings confirmed problematic gaming is most common amongst adolescent gamers who play multiplayer online games. Boys (60%) were more likely to play online games than girls (14%) and problematic gamers were more likely to be boys (5%) than girls (1%). High problematic gamers showed higher scores on depressive mood, loneliness, social anxiety, negative self-esteem, and self-reported lower school performance. Nicotine, alcohol, and cannabis using boys were almost twice more likely to report high PVG than non-users. Conclusions. It appears that online gaming in general is not necessarily associated with problems. However, problematic gamers do seem to play online games more often, and a small subgroup of gamers – specifically boys – showed lower psychosocial functioning and lower grades. Moreover, associations with alcohol, nicotine, and cannabis use are found. It would appear that problematic gaming is an undesirable problem for a small subgroup of gamers. The findings encourage further exploration of the role of psychoactive substance use in problematic gaming

Direct link between Coulomb blockade and shot noise in a quantum coherent structure

We analyze the current-voltage characteristic of a quantum conduction channel coupled to an electromagnetic environment of arbitrary frequency-dependent impedance. In the weak blockade regime the correction to the ohmic behavior is directly related to the channel current fluctuations vanishing at perfect transmission in the same way as shot noise. This relation can be generalized to describe the environmental Coulomb blockade in a generic mesoscopic conductor coupled to an external impedance, as the response of the latter to the current fluctuations in the former.Comment: 12 pages, 2 figures, submitted to Phys. Rev. Let