Condensation in ideal Fermi gases

I investigate the possibility of condensation in ideal Fermi systems of general single particle density of states. For this I calculate the probability $w_{N_0}$ of having exactly $N_0$ particles in the condensate and analyze its maxima. The existence of such maxima at macroscopic values of $N_0$ indicates a condensate. An interesting situation occurs for example in 1D systems, where $w_{N_0}$ may have two maxima. One is at $N_0=0$ and another one may exist at finite $N_0$ (for temperatures bellow a certain condensation temperature). This suggests the existence of a first order phase transition. % The calculation of $w_{N_0}$ allows for the exploration of ensemble equivalence of Fermi systems from a new perspective.Comment: 8 pages with 1 figure. Will appear in J. Phys. A: Math. Gen. Changes (minor): I updated Ref. [9] and its citation in the text. I introduced citation for figure 1 in the tex

A systematic review and recommendations on the use of plasma EBV DNA for nasopharyngeal carcinoma

Introduction: Nasopharyngeal carcinoma (NPC) is an endemic malignancy in Southeast Asia, particularly Southern China. The classical non-keratinising cell type is almost unanimously associated with latent Epstein-Barr virus (EBV) infection. Circulating plasma EBV DNA can be a useful biomarker in various clinical aspects, but comprehensive recommendations and international guidelines are still lacking. We conducted a systematic review of all original articles on the clinical application of plasma EBV DNA for NPC; we further evaluated its strengths and limitations for consideration as standard recommendations. Methods: The search terms 'nasopharyngeal OR nasopharynx', and 'plasma EBV DNA OR cell-free EBV OR cfEBV' were used to identify full-length articles published up to December 2020 in the English literature. Three authors independently reviewed the article titles, removed duplicates and reviewed the remaining articles for eligibility. Results: A total of 81 articles met the eligibility criteria. Based on the levels of evidence and grades of recommendation assessed, it is worth considering the inclusion of plasma EBV DNA in screening, pre-treatment work-up for enhancing prognostication and tailoring of treatment strategy, monitoring during radical treatment, post-treatment surveillance for early detection of relapse, and monitoring during salvage treatment for recurrent or metastatic NPC. One major limitation is the methodology of measurement requiring harmonisation for consistent comparability. Conclusions: The current comprehensive review supports the inclusion of plasma EBV DNA in international guidelines in the clinical aspects listed, but methodological issues must be resolved before global application. 2021 Elsevier Ltd. All rights reserved

Dimensionality effects in restricted bosonic and fermionic systems

The phenomenon of Bose-like condensation, the continuous change of the dimensionality of the particle distribution as a consequence of freezing out of one or more degrees of freedom in the low particle density limit, is investigated theoretically in the case of closed systems of massive bosons and fermions, described by general single-particle hamiltonians. This phenomenon is similar for both types of particles and, for some energy spectra, exhibits features specific to multiple-step Bose-Einstein condensation, for instance the appearance of maxima in the specific heat. In the case of fermions, as the particle density increases, another phenomenon is also observed. For certain types of single particle hamiltonians, the specific heat is approaching asymptotically a divergent behavior at zero temperature, as the Fermi energy $\epsilon_{\rm F}$ is converging towards any value from an infinite discrete set of energies: ${\epsilon_i}_{i\ge 1}$. If $\epsilon_{\rm F}=\epsilon_i$, for any i, the specific heat is divergent at T=0 just in infinite systems, whereas for any finite system the specific heat approaches zero at low enough temperatures. The results are particularized for particles trapped inside parallelepipedic boxes and harmonic potentials. PACS numbers: 05.30.Ch, 64.90.+b, 05.30.Fk, 05.30.JpComment: 7 pages, 3 figures (included

Ground States of Two-Dimensional Polyampholytes

We perform an exact enumeration study of polymers formed from a (quenched) random sequence of charged monomers $\pm q_0$, restricted to a 2-dimensional square lattice. Monomers interact via a logarithmic (Coulomb) interaction. We study the ground state properties of the polymers as a function of their excess charge $Q$ for all possible charge sequences up to a polymer length N=18. We find that the ground state of the neutral ensemble is compact and its energy extensive and self-averaging. The addition of small excess charge causes an expansion of the ground state with the monomer density depending only on $Q$. In an annealed ensemble the ground state is fully stretched for any excess charge $Q>0$.Comment: 6 pages, 6 eps figures, RevTex, Submitted to Phys. Rev.

A Novel DPYD Variant Associated With Severe Toxicity of Fluoropyrimidines: Role of Pre-emptive DPYD Genotype Screening

Background: The fluoropyrimidine anticancer drug, especially 5- fluorouracil (5-FU) and its prodrug capecitabine are still being the backbone of chemotherapeutic regimens for colorectal cancer. Dihydropyrimidine dehydrogenase (DPD) is the crucial enzyme in the catabolism of 5-FU. Over the past 30 years, there is substantial clinical evidence showing that DPD deficiency is strongly associated with severe and fatal fluoropyrimidine-induced toxicity.Patients and methods: A 49-year-old lady with resected stage III carcinoma of sigmoid colon was scheduled to have a course of 5-FU based adjuvant chemotherapy. She developed unexpected acute severe (grade 4) toxicity after the first cycle of chemotherapy. Genomic DNA was isolated from 3 ml peripheral blood cells for full sequencing of DPYD (the gene encoding DPD).Results: Exome sequencing confirmed that she is heterozygous for NM_000110.3: c.321+2T>C of the DPYD gene. To the best of our knowledge, this variant is a novel pathogenic splicing variant of the DPYD gene resulting in a non-functional allele. As she has a heterozygous genotype and considered having decreased DPD activity, we followed the international recommendation and restart chemotherapy with at least 50% reduction for 5-FU dose. We then titrated the 5-FU dose, and she tolerated the subsequent cycles of chemotherapy and completed the whole course of adjuvant chemotherapy.Conclusions: With a pre-emptive test on DPD deficiency before the administration of the fluoropyrimidine drugs, the aforementioned patient's life-threatening event could be avoided. This clinical utility has been confirmed by two recent large-scale studies and called for a drug label update

The Selective Role of Open and Endoscopic Approaches for Sinonasal Malignant Tumours

Endoscopic endonasal surgery has been demonstrated to be effective in the treatment of selected cases of sinonasal cancers. However, in cases of locally advanced neoplasms, as well as recurrences, the most appropriate approach is still debated. The present review aims to summarize the current state of knowledge on the utility of open approaches to resect sinonasal malignant tumours. Published comparative studies and meta-analyses suggest comparable oncological results with lower morbidity for the endoscopic approaches, but selection biases cannot be excluded. After a critical analysis of the available literature, it can be concluded that endoscopic surgery for selected lesions allows for oncologically safe resections with decreased morbidity. However, when endoscopic endonasal surgery is contraindicated and definitive chemoradiotherapy is not appropriate, craniofacial and transfacial approaches remain the best therapeutic option.Peer reviewe

Hot Spots and Transition from d-Wave to Another Pairing Symmetry in the Electron-Doped Cuprate Superconductors

We present a simple theoretical explanation for a transition from d-wave to another superconducting pairing observed in the electron-doped cuprates. The d_{x^2-y^2} pairing potential Delta, which has the maximal magnitude and opposite signs at the hot spots on the Fermi surface, becomes suppressed with the increase of electron doping, because the hot spots approach the Brillouin zone diagonals, where Delta vanishes. Then, the d_{x^2-y^2} pairing is replaced by either singlet s-wave or triplet p-wave pairing. We argue in favor of the latter and discuss experiments to uncover it.Comment: 6 pages, 4 figures, RevTeX 4. V.2: Extra figure and many references added. V.3: Minor update of references for the proof

Midgap edge states and pairing symmetry of quasi-one-dimensional organic superconductors

The singlet s-, d- and triplet p-wave pairing symmetries in quasi-one-dimensional organic superconductors can be experimentally discriminated by probing the Andreev bound states at the sample edges. These states have the energy in the middle of the superconducting gap and manifest themselves as a zero-bias peak in tunneling conductance into the corresponding edge. Their existence is related to the sign change of the pairing potential around the Fermi surface. We present an exact self-consistent solution of the edge problem showing the presence of the midgap states for p_x-wave superconductivity. The spins of the edge state respond paramagnetically to a magnetic field parallel to the vector d that characterizes triplet pairing.Comment: 6 pages, 4 figures. V.2: New section on spin response is added and references are updated. V.3: Final version accepted to PRB. Typos are corrected and important note is added in proof

Parquet solution for a flat Fermi surface

We study instabilities occurring in the electron system whose Fermi surface has flat regions on its opposite sides. Such a Fermi surface resembles Fermi surfaces of some high-$T_c$ superconductors. In the framework of the parquet approximation, we classify possible instabilities and derive renormalization-group equations that determine the evolution of corresponding susceptibilities with decreasing temperature. Numerical solutions of the parquet equations are found to be in qualitative agreement with a ladder approximation. For the repulsive Hubbard interaction, the antiferromagnetic (spin-density-wave) instability dominates, but when the Fermi surface is not perfectly flat, the $d$-wave superconducting instability takes over.Comment: REVTeX, 36 pages, 20 ps figures inserted via psfig. Submitted to Phys. Rev.

Electrical properties of ferroelectric YMnO3 films deposited on n-type Si (111) substrates

YMnO3 thin films were grown on n - type Si substrate by nebulized spray pyrolysis in Metal - Ferroelectric - Semiconductor (MFS) configuration. The C-V characteristics of the film in MFS structure exhibit hysteretic behavior consistent with the polarization charge switching direction, with the memory window decreasing with increase in temperature. The density of interface states decreases with the increase in the annealing temperature. Mapping of the silicon energy band gap with the interface states has been carried out. The leakage current measured in the accumulation region, is lower in well-crystallized thin films and obeys a space- charge limited conduction mechanism. The calculated activation energy from the dc leakage current characteristics of Arhennius plot reveals that the activation energy correspond to the oxygen vacancy motionComment: 26 pages, 1 table, 8 figures, submitted to submitted to J. Phys. D; applied physics on 5th feb 200