Local Tunneling Study of Three-Dimensional Order Parameter in the π\pi-band of Al-doped MgB2_2 Single Crystals

We have performed local tunneling spectroscopy on high quality Mg$_{1-x}$Al$_x$B$_2$ single crystals by means of Variable Temperature Scanning Tunneling Spectroscopy (STS) in magnetic field up to 3 Tesla. Single gap conductance spectra due to c-axis tunneling were extensively measured, probing different amplitudes of the three-dimensional $\Delta_\pi$ as a function of Al content. Temperature and magnetic field dependences of the conductance spectra were studied in S-I-N configuration: the effect of the doping resulted in a monotonous reduction of the locally measured $T_C$ down to 24K for x=0.2. On the other hand, we have found that the gap amplitude shows a maximum value $\Delta_\pi= 2.3$ meV for x=0.1, while the $\Delta_\pi / T_C$ ratio increases monotonously with doping. The locally measured upper critical field was found to be strongly related to the gap amplitude, showing the maximum value $H_{c2}\simeq3T$ for x=0.1 substituted samples. For this Al concentration the data revealed some spatial inhomogeneity in the distribution of $\Delta_\pi$ on nanometer scale.Comment: 4 pages, 3 figure

Probing the superconducting condensate on a nanometer scale

Superconductivity is a rare example of a quantum system in which the wavefunction has a macroscopic quantum effect, due to the unique condensate of electron pairs. The amplitude of the wavefunction is directly related to the pair density, but both amplitude and phase enter the Josephson current : the coherent tunneling of pairs between superconductors. Very sensitive devices exploit the superconducting state, however properties of the {\it condensate} on the {\it local scale} are largely unknown, for instance, in unconventional high-T$_c$ cuprate, multiple gap, and gapless superconductors. The technique of choice would be Josephson STS, based on Scanning Tunneling Spectroscopy (STS), where the condensate is {\it directly} probed by measuring the local Josephson current (JC) between a superconducting tip and sample. However, Josephson STS is an experimental challenge since it requires stable superconducting tips, and tunneling conditions close to atomic contact. We demonstrate how these difficulties can be overcome and present the first spatial mapping of the JC on the nanometer scale. The case of an MgB$_2$ film, subject to a normal magnetic field, is considered.Comment: 7 pages, 6 figure

Exact analytical evaluation of time dependent transmission coefficient from the method of reactive flux for an inverted parabolic barrier

In this paper we derive a general expression for the transmission coefficient using the method of reactive flux for a particle coupled to a harmonic bath surmounting a one dimensional inverted parabolic barrier. Unlike Kohen and Tannor [J. Chem. Phys. 103, 6013 (1995)] we use a normal mode analysis where the unstable and the other modes have a complete physical meaning. Importantly our approach results a very general expression for the time dependent transmission coefficient not restricted to overdamped limit. Once the spectral density for the problem is know one can use our formula to evaluate the time dependent transmission coefficient. We have done the calculations with time dependent friction used by Xie [Phys. Rev. Lett 93, 180603 (2004)] and also the one used by Kohen and Tannor [J. Chem. Phys. 103, 6013 (1995)]. Like the formula of Kohen and Tannor our formula also reproduces the results of transition state theory as well as the Kramers theory in the limits t->0 and t->infinity respectively

Probing the superfluid velocity with a superconducting tip: the Doppler shift effect

We address the question of probing the supercurrents in superconducting (SC) samples on a local scale by performing Scanning Tunneling Spectroscopy (STS) experiments with a SC tip. In this configuration, we show that the tunneling conductance is highly sensitive to the Doppler shift term in the SC quasiparticle spectrum of the sample, thus allowing the local study of the superfluid velocity. Intrinsic screening currents, such as those surrounding the vortex cores in a type II SC in a magnetic field, are directly probed. With Nb tips, the STS mapping of the vortices, in single crystal 2H-NbSe_2, reveals both the vortex cores, on the scale of the SC coherence length $\xi$, and the supercurrents, on the scale of the London penetration length $\lambda$. A subtle interplay between the SC pair potential and the supercurrents at the vortex edge is observed. Our results open interesting prospects for the study of screening currents in any superconductor.Comment: 4 pages, 5 figure

Metal-semiconductor-metal photodetectors on a GeSn-on-insulator platform for 2 µm applications

In this work, the metal-semiconductor-metal photodetectors were demonstrated on the Ge0.91Sn0.09-on-insulator (GeSnOI) platform. The responsivity was 0.24 and 0.06 A/W at wavelengths of 1,600 and 2,003 nm, respectively. Through a systematic study, it is revealed that the photodetectors can potentially detect wavelength beyond 2,200 nm. The dark current density was measured to be 4.6 A/cm2 for GeSnOI waveguide-shaped photodetectors. The 3 dB bandwidth was observed to be 1.26 and 0.81 GHz at 1,550 and 2,000 nm wavelengths, respectively. This work opens up an opportunity for low-cost 2 µm wavelength photodetection on the GeSn/Ge interface-free GeSnOI platform

Reply to Comment on "Completely positive quantum dissipation"

This is the reply to a Comment by R. F. O'Connell (Phys. Rev. Lett. 87 (2001) 028901) on a paper written by the author (B. Vacchini, ``Completely positive quantum dissipation'', Phys.Rev.Lett. 84 (2000) 1374, arXiv:quant-ph/0002094).Comment: 2 pages, revtex, no figure

Perception about the importance of feeding in a group of hematologic cancer patients

Introducción: Los pacientes oncohematológicos presentan habitualmente déficits nutricionales derivados de su enfermedad, sus tratamientos y efectos secundarios, etc. Sin embargo, apenas existen datos descriptivos del empleo de recomendaciones dietéticas, y de la auto-percepción del paciente de su utilidad en su enfermedad. Objetivos: Evaluar la percepción de la importancia de la alimentación en un grupo de pacientes con cáncer hematológico. Materiales y métodos: 111 pacientes oncohematológicos auto-registraron un cuestionario con preguntas sociosanitarias y de percepción personal de la importancia de la alimentación en su enfermedad. Resultados: La edad media fue 40,0 ± 12,8 años (64,86% mujeres). El diagnóstico y el tratamiento más frecuente fue linfoma (83,78%) y quimioterapia (92,80%). Un 75% consideró “muy importante” la relación entre enfermedad oncohematológica y estado nutricional. Sólo un 54,1% recibió consejo dietético. Y un 53,2% y 50,5% consideró que el consumo de suplementos nutricionales mejoraría su calidad de vida y/o enfermedad respectivamente. Conclusiones: Un porcentaje importante de pacientes presentaron estados avanzados de su enfermedad. Sin embargo, la mitad del colectivo no había recibido pautas dietéticas a pesar del elevado interés por recibir atención nutricional. Por tanto, la valoración nutricional del paciente oncohematológico así como la implementación de un soporte nutricional personalizado deberían formar parte de la práctica clínica habitualIntroduction: Oncohematologic patients usually present nutritional deficits associated with the disease, the treatments and side effects, etc. However, there are hardly any descriptive data about the dietary recommendations used and the patient’s self-perception of its usefulness in their disease. Aim: To assess the self-perception of the nutritional importance in a group of oncohematologic patients. Materials and methods: 111 oncohematologic patients self-reported a questionnaire containing items about socio-sanitary data and self-perception of the nutritional importance in their disease. Results: The mean age was 40.0 ± 12.8 years (64.86% women). The most frequent diagnosis and treatment was lymphoma (83.78%) and chemoteraphy (92.80%). 75% considered “very important” relationship between oncohematologic disease and nutritional status. Only 54.1% received dietary advice. And 53.2% and 50.5% considered that the use of nutritional supplements improve quality of life and/or disease respectively. Conclusions: A significant percentage of patients had advanced stages of their disease. However, half the group had not received dietary advice despite high interest in receiving nutritional care. Therefore, the nutritional assessment and the personalized nutritional support implementation of the patient should be included in routine clinical practic

Exploring the use of a participative design in the early development of a predictive test : the importance of physician involvement

In this study, we contribute to the personalized medicine and health care management literature by developing and testing a new participative design approach. We propose that involving gastroenterologists in the development of a predictive test to assist them in their clinical decision-making process for the treatment of inflammatory bowel diseases will increase the likelihood of their acceptance of the innovation. Based on data obtained from 6 focus groups across Canada from a total of 28 physicians, analyses reveal that current tools do not enable discriminating between treatment options to find the best fit for each patient. Physicians expect a new predictive tool to have the capability of showing clear reliability and significant benefits for the patient, while being accessible in a timely manner that facilitates clinical decisions. Physicians also insist on their key role in the implementation process, hence confirming the relevance and importance of participative designs in personalized medicine

Patients’ perception of their involvement in shared treatment decision making : key factors in the treatment of inflammatory bowel disease

Objectives This study aims to characterize the relationships between the quality of the information given by the physician, the involvement of the patient in shared decision making (SDM), and outcomes in terms of satisfaction and anxiety pertaining to the treatment of inflammatory bowel disease (IBD). Methods A Web survey was conducted among 200 Canadian patients affected with IBD. The theoretical model of SDM was adjusted using path analysis. SAS software was used for all statistical analyses. Results The quality of the knowledge transfer between the physician and the patient is significantly associated with the components of SDM: information comprehension, patient involvement and decision certainty about the chosen treatment. In return, patient involvement in SDM is significantly associated with higher satisfaction and, as a result, lower anxiety as regards treatment selection. Conclusions This study demonstrates the importance of involving patients in shared treatment decision making in the context of IBD. Practice implications Understanding shared decision making may motivate patients to be more active in understanding the relevant information for treatment selection, as it is related to their level of satisfaction, anxiety and adherence to treatment. This relationship should encourage physicians to promote shared decision making