Superconductivity in the repulsive Hubbard model: an asymptotically exact weak-coupling solution

We study the phase diagram of the Hubbard model in the limit where U, the onsite repulsive interaction, is much smaller than the bandwidth. We present an asymptotically exact expression for T$_c$, the superconducting transition temperature, in terms of the correlation functions of the non-interacting system which is valid for arbitrary densities so long as the interactions are sufficiently small. Our strategy for computing T$_c$ involves first integrating out all degrees of freedom having energy higher than an unphysical initial cutoff $\Omega_0$. Then, the renormalization group (RG) flows of the resulting effective action are computed and T$_c$ is obtained by determining the scale below which the RG flows in the Cooper channel diverge. We prove that T$_c$ is independent of $\Omega_0$. Using this method, we find a variety of unconventional superconducting ground states in two and three dimensional lattice systems and present explicit results for T$_c$ and pairing symmetries as a function of the electron concentration.Comment: 18 pages, 17 figure

Topological Quantum Computation on Supersymmetric Spin Chains

Quantum gates built out of braid group elements form the building blocks of topological quantum computation. They have been extensively studied in SU(2)k quantum group theories, a rich source of examples of non-Abelian anyons such as the Ising (k=2), Fibonacci (k=3) and Jones-Kauffman (k=4) anyons. We show that the fusion spaces of these anyonic systems can be precisely mapped to the product state zero modes of certain Nicolai-like supersymmetric spin chains. As a result, we can realize the braid group on the product state zero modes of these supersymmetric systems. These operators kill all the other states in the Hilbert space, thus preventing the occurrence of errors while processing information, making them suitable for quantum computing

Postprostatectomy Erectile Dysfunction: A Review

In the current era of the early diagnosis of prostate cancer (PCa) and the development of minimally invasive surgical techniques, erectile dysfunction (ED) represents an important issue, with up to 68% of patients who undergo radical prostatectomy (RP) complaining of postoperative erectile function (EF) impairment. In this context, it is crucial to comprehensively consider all factors possibly associated with the prevention of post-RP ED throughout the entire clinical management of PCa patients. A careful assessment of both oncological and functional baseline characteristics should be carried out for each patient preoperatively. Baseline EF, together with age and the overall burden of comorbidities, has been strongly associated with the chance of post-RP EF recovery. With this goal in mind, internationally validated psychometric instruments are preferable for ensuring proper baseline EF evaluations, and questionnaires should be administered at the proper time before surgery. Careful preoperative counselling is also required, both to respect the patient's wishes and to avoid false expectations regarding eventual recovery of baseline EF. The advent of robotic surgery has led to improvements in the knowledge of prostate surgical anatomy, as reflected by the formal redefinition of nerve-sparing techniques. Overall, comparative studies have shown significantly better EF outcomes for robotic RP than for open techniques, although data from prospective trials have not always been consistent. Preclinical data and several prospective randomized trials have demonstrated the value of treating patients with oral phosphodiesterase 5 inhibitors (PDE5is) after surgery, with the concomitant potential benefit of early re-oxygenation of the erectile tissue, which appears to be crucial for avoiding the eventual penile structural changes that are associated with postoperative neuropraxia and ultimately result in severe ED. For patients who do not properly respond to PDE5is, proper counselling regarding intracavernous treatment should be considered, along with the further possibility of surgical treatment for ED involving the implantation of a penile prosthesis

Single-site entanglement at superconductor-insulator transition in the Hirsch model

We investigate the transition to the insulating state in the one-dimensional Hubbard model with bond-charge interaction x (Hirsch model), at half-filling and T=0. By means of the density-matrix renormalization group algorithm the charge gap closure is examined by both standard finite size scaling analysis and looking at singularities in the derivatives of single-site entanglement. The results of the two techniques show that a quantum phase transition takes place at a finite Coulomb interaction u_c(x) for x>0.5. The region 0<u<u_c turns out to have a superconducting nature, at least for not too large x>x_c.Comment: 5 pages, 6 figure

Orgasmic Dysfunction after Radical Prostatectomy

In addition to urinary incontinence and erectile dysfunction, several other impairments of sexual function potentially occurring after radical prostatectomy (RP) have been described; as a whole, these less frequently assessed disorders are referred to as neglected side effects. In particular, orgasmic dysfunctions (ODs) have been reported in a non-negligible number of cases, with detrimental impacts on patients' overall sexual life. This review aimed to comprehensively discuss the prevalence and physiopathology of post-RP ODs, as well as potential treatment options. Orgasm-associated incontinence (climacturia) has been reported to occur in between 20% and 93% of patients after RP. Similarly, up to 19% of patients complain of postoperative orgasm-associated pain, mainly referred pain at the level of the penis. Moreover, impairment in the sensation of orgasm or even complete anorgasmia has been reported in 33% to 77% of patients after surgery. Clinical and surgical factors including age, the use of a nerve-sparing technique, and robotic surgery have been variably associated with the risk of ODs after RP, although robust and reliable data allowing for a proper estimation of the risk of postoperative orgasmic function impairment are still lacking. Likewise, little evidence regarding the management of postoperative ODs is currently available. In general, physicians should be aware of the prevalence of ODs after RP, in order to properly counsel all patients both preoperatively and immediately post-RP about the potential occurrence of bothersome and distressful changes in their overall sexual function

Current status of local penile therapy

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Clinical significance of erectile dysfunction developing after acute coronary event : exception to the rule or confirmation of the artery size hypothesis?

Erectile dysfunction (ED) has been found to frequently precedes the onset of coronary artery disease (CAD), representing an early marker of subclinical vascular disease, included CAD. Its recognition is, therefore, a "window opportunity" to prevent a coronary event by aggressive treatment of cardiovascular risk factors. The artery size hypothesis (ASH) has been proposed as a putative mechanism to explain the relationship between ED and CAD. Since atherosclerosis is a systemic disorder all major vascular beds should be affected to the same extent. However, symptoms at different points in the system rarely become evident at the same time. This is likely the result of smaller vessels (i.e. the penile artery) being able to less well tolerate the same amount of plaque when compared with larger ones (i.e. the coronary artery). If true, ED will develop before CAD. We present a case in which ED developed after a coronary event yet before a coronary recurrence potentially representing a late marker of vascular progression. Reasons for this unusual sequence are discussed as they might still fit the ASH

Apomorphine-induced brain modulation during sexual stimulation: a new look at central phenomena related to erectile dysfunction

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