Quasi-one-dimensional system as a high-temperature superconductor

It is well-known that quasi-one-dimensional superconductors suffer from the pairing fluctuations that significantly reduce the superconducting temperature or even completely suppress any coherent behavior. Here we demonstrate that a coupling to a robust pair condensate changes the situation dramatically. In this case the quasi-one-dimensional system can be a high temperature superconductor governed by the proximity to the Lifshitz transition at which the Fermi level approaches the lower edge of the single-particle spectrum.Comment: 5 pages, 1 figur

Dynamics and energy spectra of aperiodic discrete-time quantum walks

We investigate the role of different aperiodic sequences in the dynamics of single quantum particles in discrete space and time. For this we consider three aperiodic sequences, namely, the Fibonacci, Thue-Morse, and Rudin-Shapiro sequences, as examples of tilings the diffraction spectra of which have pure point, singular continuous, and absolutely continuous support, respectively. Our interest is to understand how the order, intrinsically introduced by the deterministic rule used to generate the aperiodic sequences, is reflected in the dynamical properties of the quantum system. For this system we consider a single particle undergoing a discrete-time quantum walk (DTQW), where the aperiodic sequences are used to distribute the coin operations at different lattice positions (inhomogeneous DTQW) or by applying the same coin operation at all lattice sites at a given time but choosing different coin operation at each time step according to the chosen aperiodic sequence (time dependent DTQW). We study the energy spectra and the spreading of an initially localized wave packet for different cases, finding that in the case of Fibonacci and Thue-Morse tilings the system is superdiffusive, whereas in the Rudin-Shapiro case it is strongly subdiffusive. Trying to understand this behavior in terms of the energy spectra, we look at the survival amplitude as a function of time. By means of the echo we present strong evidence that, although the three orderings are very different as evidenced by their diffraction spectra, the energy spectra are all singular continuous except for the inhomogeneous DTQW with the Rudin-Shapiro sequence where it is discrete. This is in agreement with the observed strong localization both in real space and in the Hilbert space. Our paper is particularly interesting because quantum walks can be engineered in laboratories by means of ultracold gases or in optical waveguides, and therefore would be a perfect playground to study singular continuous energy spectra in a completely controlled quantum setup

Elastic constant dishomogeneity and Q2Q^2 dependence of the broadening of the dynamical structure factor in disordered systems

We propose an explanation for the quadratic dependence on the momentum $Q$, of the broadening of the acoustic excitation peak recently found in the study of the dynamic structure factor of many real and simulated glasses. We ascribe the observed $Q^2$ law to the spatial fluctuations of the local wavelength of the collective vibrational modes, in turn produced by the dishomegeneity of the inter-particle elastic constants. This explanation is analitically shown to hold for 1-dimensional disordered chains and satisfatorily numerically tested in both 1 and 3 dimensions.Comment: 4 pages, RevTeX, 5 postscript figure

Vibrational spectrum of topologically disordered systems

The topological nature of the disorder of glasses and supercooled liquids strongly affects their high-frequency dynamics. In order to understand its main features, we analytically studied a simple topologically disordered model, where the particles oscillate around randomly distributed centers, interacting through a generic pair potential. We present results of a resummation of the perturbative expansion in the inverse particle density for the dynamic structure factor and density of states. This gives accurate results for the range of densities found in real systems.Comment: Completely rewritten version, accepted in Physical Review Letter

Relaxation processes in harmonic glasses?

A relaxation process, with the associated phenomenology of sound attenuation and sound velocity dispersion, is found in a simulated harmonic Lennard-Jones glass. We propose to identify this process with the so called microscopic (or instantaneous) relaxation process observed in real glasses and supercooled liquids. A model based on the memory function approach accounts for the observation, and allows to relate to each others: 1) the characteristic time and strength of this process, 2) the low frequency limit of the dynamic structure factor of the glass, and 3) the high frequency sound attenuation coefficient, with its observed quadratic dependence on the momentum transfer.Comment: 11 pages, 3 figure

Systematic aortic and pelvic lymphadenectomy versus resection of bulky nodes only in optimally debulked advanced ovarian cancer: A randomized clinical trial

The role of systematic aortic and pelvic lymphadenectomy in patients with optimally debulked advanced ovarian cancer is unclear and has not been addressed by randomized studies. We conducted a randomized clinical trial to determine whether systematic aortic and pelvic lymphadenectomy improves progression-free and overall survival compared with resection of bulky nodes only. Methods: From January 1991 through May 2003, 427 eligible patients with International Federation of Gynecology and Obstetrics (FIGO) stage IIIB-C and IV epithelial ovarian carcinoma were randomly assigned to undergo systematic pelvic and para-aortic lymphadenectomy (n = 216) or resection of bulky nodes only (n = 211). Progression-free survival and overall survival were analyzed using a logrank statistic and a Cox multivariable regression analysis. All statistical tests were two-sided. Results: After a median followup of 68.4 months, 292 events (i.e., recurrences or deaths) were observed, and 202 patients had died. Sites of first recurrences were similar in both arms. The adjusted risk for first event was statistically significantly lower in the systematic lymphadenectomy arm (hazard ratio [HR] =.75, 95% confidence interval [CI] = 0.59 to 0.94; P =.01) than in the no-lymphadenectomy arm, corresponding to 5-year progression-free survival rates of 31.2 and 21.6% in the systematic lymphadenectomy and control arms, respectively (difference = 9.6%, 95% CI = 1.5% to 21.6%), and to median progression-free survival of 29.4 and 22.4 months, respectively (difference = 7 months, 95% CI = 1.0 to 14.4 months). The risk of death was similar in both arms (HR = 0.97, 95% CI = 0.74 to 1.29; P =.85), corresponding to 5-year overall survival rates of 48.5 and 47%, respectively (difference = 1.5%, 95% CI = -8.4% to 10.6%), and to median overall survival of 58.7 and 56.3 months, respectively (difference = 2.4 months, 95% CI = -11.8 to 21.0 months). Median operating time was longer, and the percentage of patients requiring blood transfusions was higher in the systematic lymphadenectomy arm than in the no-lymphadenectomy arm (300 versus 210 minutes, P <.001, and 72% versus 59%; P =.006, respectively). Conclusion: Systematic lymphadenectomy improves progression-free but not overall survival in women with optimally debulked advanced ovarian carcinoma

Properties of Graphene: A Theoretical Perspective

In this review, we provide an in-depth description of the physics of monolayer and bilayer graphene from a theorist's perspective. We discuss the physical properties of graphene in an external magnetic field, reflecting the chiral nature of the quasiparticles near the Dirac point with a Landau level at zero energy. We address the unique integer quantum Hall effects, the role of electron correlations, and the recent observation of the fractional quantum Hall effect in the monolayer graphene. The quantum Hall effect in bilayer graphene is fundamentally different from that of a monolayer, reflecting the unique band structure of this system. The theory of transport in the absence of an external magnetic field is discussed in detail, along with the role of disorder studied in various theoretical models. We highlight the differences and similarities between monolayer and bilayer graphene, and focus on thermodynamic properties such as the compressibility, the plasmon spectra, the weak localization correction, quantum Hall effect, and optical properties. Confinement of electrons in graphene is nontrivial due to Klein tunneling. We review various theoretical and experimental studies of quantum confined structures made from graphene. The band structure of graphene nanoribbons and the role of the sublattice symmetry, edge geometry and the size of the nanoribbon on the electronic and magnetic properties are very active areas of research, and a detailed review of these topics is presented. Also, the effects of substrate interactions, adsorbed atoms, lattice defects and doping on the band structure of finite-sized graphene systems are discussed. We also include a brief description of graphane -- gapped material obtained from graphene by attaching hydrogen atoms to each carbon atom in the lattice.Comment: 189 pages. submitted in Advances in Physic

Randomised study of systematic lymphadenectomy in patients with epithelial ovarian cancer macroscopically confined to the pelvis

No randomised trials have addressed the value of systematic aortic and pelvic lymphadenectomy (SL) in ovarian cancer macroscopically confined to the pelvis. This study was conducted to investigate the role of SL compared with lymph nodes sampling (CONTROL) in the management of early stage ovarian cancer. A total of 268 eligible patients with macroscopically intrapelvic ovarian carcinoma were randomised to SL (N=138) or CONTROL (N=130). The primary objective was to compare the proportion of patients with retroperitoneal nodal involvement between the two groups. Median operating time was longer and more patients required blood transfusions in the SL arm than the CONTROL arm (240 vs 150 min, P<0.001, and 36 vs 22%, P=0.012, respectively). More patients in the SL group had positive nodes at histologic examination than patients on CONTROL (9 vs 22%, P=0.007). Postoperative chemotherapy was delivered in 66% and 51% of patients with negative nodes on CONTROL and SL, respectively (P=0.03). At a median follow-up of 87.8 months, the adjusted risks for progression (hazard ratio [HR]=0.72, 95%CI=0.46–1.21, P=0.16) and death (HR=0.85, 95%CI=0.49–1.47, P=0.56) were lower, but not statistically significant, in the SL than the CONTROL arm. Five-year progression-free survival was 71.3 and 78.3% (difference=7.0%, 95% CI=–3.4–14.3%) and 5-year overall survival was 81.3 and 84.2% (difference=2.9%, 95% CI=−7.0–9.2%) respectively for CONTROL and SL. SL detects a higher proportion of patients with metastatic lymph nodes. This trial may have lacked power to exclude clinically important effects of SL on progression free and overall survival

Long-term outcome of COVID-19 patients treated with helmet noninvasive ventilation vs. high-flow nasal oxygen: a randomized trial

Background: Long-term outcomes of patients treated with helmet noninvasive ventilation (NIV) are unknown: safety concerns regarding the risk of patient self-inflicted lung injury and delayed intubation exist when NIV is applied in hypoxemic patients. We assessed the 6-month outcome of patients who received helmet NIV or high-flow nasal oxygen for COVID-19 hypoxemic respiratory failure. Methods: In this prespecified analysis of a randomized trial of helmet NIV versus high-flow nasal oxygen (HENIVOT), clinical status, physical performance (6-min-walking-test and 30-s chair stand test), respiratory function and quality of life (EuroQoL five dimensions five levels questionnaire, EuroQoL VAS, SF36 and Post-Traumatic Stress Disorder Checklist for the DSM) were evaluated 6&nbsp;months after the enrollment. Results: Among 80 patients who were alive, 71 (89%) completed the follow-up: 35 had received helmet NIV, 36 high-flow oxygen. There was no inter-group difference in any item concerning vital signs (N = 4), physical performance (N = 18), respiratory function (N = 27), quality of life (N = 21) and laboratory tests (N = 15). Arthralgia was significantly lower in the helmet group (16% vs. 55%, p = 0.002). Fifty-two percent of patients in helmet group vs. 63% of patients in high-flow group had diffusing capacity of the lungs for carbon monoxide &lt; 80% of predicted (p = 0.44); 13% vs. 22% had forced vital capacity &lt; 80% of predicted (p = 0.51). Both groups reported similar degree of pain (p = 0.81) and anxiety (p = 0.81) at the EQ-5D-5L test; the EQ-VAS score was similar in the two groups (p = 0.27). Compared to patients who successfully avoided invasive mechanical ventilation (54/71, 76%), intubated patients (17/71, 24%) had significantly worse pulmonary function (median diffusing capacity of the lungs for carbon monoxide 66% [Interquartile range: 47–77] of predicted vs. 80% [71–88], p = 0.005) and decreased quality of life (EQ-VAS: 70 [53–70] vs. 80 [70–83], p = 0.01). Conclusions: In patients with COVID-19 hypoxemic respiratory failure, treatment with helmet NIV or high-flow oxygen yielded similar quality of life and functional outcome at 6&nbsp;months. The need for invasive mechanical ventilation was associated with worse outcomes. These data indicate that helmet NIV, as applied in the HENIVOT trial, can be safely used in hypoxemic patients. Trial registration Registered on clinicaltrials.gov NCT04502576 on August 6, 202