Islanding, growth mode and ordering in Si heteroepitaxy on Ge(001) substrates structured by thermal annealing

Si/Ge heteroepitaxial dots under tensile strain are grown on nanostructured Ge substrates produced by high-temperature flash heating exploiting the spontaneous faceting of the Ge(001) surface close to the onset of surface melting. A very diverse growth mode is obtained depending on the specific atomic structure and step density of nearby surface domains with different vicinal crystallographic orientations. On highly-miscut areas of the Ge(001) substrate, the critical thickness for islanding is lowered to about 5 ML, in contrast to the 11 ML reported for the flat Ge(001) surface, while on unreconstructed (1x1) domains the growth is Volmer-Weber driven. An explanation is proposed considering the diverse relative contributions of step and surface energies on misoriented substrates. In addition, we show that the bottom-up pattern of the substrate naturally formed by thermal annealing determines a spatial correlation for the dot sites

Low field magnetotransport in strained Si/SiGe cavities

Low field magnetotransport revealing signatures of ballistic transport effects in strained Si/SiGe cavities is investigated. We fabricated strained Si/SiGe cavities by confining a high mobility Si/SiGe 2DEG in a bended nanowire geometry defined by electron-beam lithography and reactive ion etching. The main features observed in the low temperature magnetoresistance curves are the presence of a zero-field magnetoresistance peak and of an oscillatory structure at low fields. By adopting a simple geometrical model we explain the oscillatory structure in terms of electron magnetic focusing. A detailed examination of the zero-field peak lineshape clearly shows deviations from the predictions of ballistic weak localization theory.Comment: Submitted to Physical Review B, 25 pages, 7 figure

Conductance quantization in etched Si/SiGe quantum point contacts

We fabricated strongly confined Schottky-gated quantum point contacts by etching Si/SiGe heterostructures and observed intriguing conductance quantization in units of approximately 1e2/h. Non-linear conductance measurements were performed depleting the quantum point contacts at fixed mode-energy separation. We report evidences of the formation of a half 1e2/h plateau, supporting the speculation that adiabatic transmission occurs through 1D modes with complete removal of valley and spin degeneracies.Comment: to appear in Physical Review

Appendiceal mucinous neoplasms: An uncertain nosological entity. Report of a case

Introduction: Appendiceal mucocele is a relatively rare condition characterized by progressive dilation of the appendix caused by intraluminal accumulation of mucoid substance. Its incidence is 0.07 - 0,63% of all appendectomies performed. Case report: We report the case of a 70-year-old man who came to our observation with gravative pain in right lower abdominal region. A computed tomography abdominal scan revealed a cystic/tubular structure like an appendicular mass with wall enhancement but without calcifications suggestive of a mucocele. Into peritoneal cavity we found profuse mucinous material with a 1,5 cm size parietal nodule. We also identified a free perforation of the cecum with consensual spillage of gelatinous material mimicking a pseudomyxoma peritonei. We decided to perform a right hemicolectomy with excision of peritoneal lesion. Discussion: The controversy in the pathologic terminology can give rise to a clinical dilemma in terms of the management and follow-up plans. For mucosal hyperplasia and cystadenoma simple appendectomy is curative. Only in case of large base of implantation it may be necessary the resection of the ileum and caecum or right hemicolectomy. In case of mucinous cystoadenocarcinoma authors perform a right hemicolectomy. Conclusion: Appendiceal mucinous neoplasms are different pathological entities. The correct surgical management depends on size and location of lesion. A preoperative diagnosis is obviously needed in order to perform the correct treatment. CT abdominal scan is the better diagnostic tool, but different authors show their inability to reach a preoperative diagnosis in the larger majority of cases

Endometrial cancer: Robotic versus Laparoscopic treatment. Preliminary report

Laparoscopic approach is today the standard treatment for benign and malignant gynecological pathologies. To traditional laparoscopic surgery in the last 10 years we can add the possibility to use a robotic platform. The adoption of this system allows undoubted advantages as the three-dimensional vision, the absence of the physiological tremor with enhanced ergonomics and possibility of using articulable tools. In this study we analyzed the results of 18 patients with endometrial cancer (Stage I) treated with robotic approach. The results were compared with a selected sample of 26 patients, with the same characteristics, treated with traditional laparoscopic approach in the same period by the same surgical team. The mean total operative time was significantly longer for robotic than laparoscopic group (125.6 min vs 102.3 min). However, if to this operative time we remove the time of preparation (docking time) we obtain the following results: 102.5 min for robotic group and 95.7 min for the laparoscopic control group. Intra-operative blood loss are significantly lower in the robotic group than in laparoscopic group. The robotic treatment of gynecological cancer is a safe and feasible technique. The oncological results are also equivalent to those of traditional laparoscopic surgery with advantages in terms of precision and reduction of intraoperative bleeding. Additional clinical studies on larger samples and heterogeneous patients are necessary in order to clarify the real advantages of robotic treatment

Quantum states of elementary three-geometry

We introduce a quantum volume operator $K$ in three--dimensional Quantum Gravity by taking into account a symmetrical coupling scheme of three SU(2) angular momenta. The spectrum of $K$ is discrete and defines a complete set of eigenvectors which is alternative with respect to the complete sets employed when the usual binary coupling schemes of angular momenta are considered. Each of these states, that we call quantum bubbles, represents an interference of extended configurations which provides a rigorous meaning to the heuristic notion of quantum tetrahedron. We study the generalized recoupling coefficients connecting the symmetrical and the binary basis vectors, and provide an explicit recursive solution for such coefficients by analyzing also its asymptotic limit.Comment: 15 pages, LaTe

Comparison of anti-transglutaminase ELISAs and an anti-endomysial antibody assay in the diagnosis of celiac disease: A prospective study

Background: Most studies of anti-transglutaminase (anti-tTG) assays have considered preselected groups of patients. This study compared the sensitivity, specificity, and predictive value of an immunofluorescence method for anti-endomysial antibodies (EmAs) and two anti-tTG ELISAs, one using guinea pig tTG (gp-tTG) and the other human tTG (h-tTG) as antigen, in consecutive patients investigated for suspected celiac disease (CD). Methods: We studied 207 consecutive patients (99 men, 108 women; age range, 17-84 years) who underwent intestinal biopsy for suspected CD. Patients presented with one or more of the following: weight loss, anemia, chronic diarrhea, abdominal pain, dyspepsia, alternating bowel habits, constipation, pain in the joints, and dermatitis. At entry to the study, an intestinal biopsy was performed and a serum sample was taken for IgA EmAs, anti-gp-tTG, and anti-h-tTG. Results: Intestinal histology showed that 24 patients had partial or total villous atrophy; in these patients the diagnosis of CD was confirmed by follow-up. The remaining 183 patients had villous/crypt ratios that were within our laboratory's reference values and were considered controls. Serum EmAs, anti-gp-tTG, and anti-h-tTG were positive in all 24 CD patients; in the control group, none were positive for serum EmAs, but 15 of 183 (8.2%) were positive for anti-gp-tTG, and 6 of 183 (3.3%) were positive for anti-h-tTG. Sensitivity was 100% for all assays, whereas specificity was 100% for the EmA, 92% for the anti-gp-tTG, and 97% for the anti-h-tTG assay. The negative predictive value was 100% for all assays; the positive predictive value was 100% for the EmA, 80% [95% confidence interval (CI), 65-95%] for the anti-h-tTG (P = 0.03 vs EmA) and 60% (95% CI, 44-76%) for the anti-gp-tTG assay (P = 0.0002 vs EmA). Areas (95% CIs) under the ROC curves were 0.987 (0.97-1.0) for anti-h-tTG and 0.965 (0.94-0.99) for anti-gp-tTG. Most of the patients testing false positive for anti-tTG had Crohn disease or chronic liver disease. Conclusions: Although both anti-tTG ELISAs showed optimum sensitivity, their lack of specificity yielded positive predictive values significantly lower than those for the EmA assay. © 2002 American Association for Clinical Chemistry

Whipple's pancreaticoduodenectomy: Surgical technique and perioperative clinical outcomes in a single center

Introduction: Pancreatic cancer is the fourth cause of death from cancer in Western countries. The radical surgical resection is the only curative option for this pathology. The prevalence of this disease increases with age in population. The causes of pancreatic cancer are unknown, but we consider risk factors like smoke and tobacco usage, alcohol consumption coffee, history of diabetes or chronic pancreatitis. In this study we report our experience in the treatment of resectable pancreatic cancer and periampullary neoplasms with particular attention to evaluate the evolution of surgical technique and the clinical postoperative outcomes. Methods: In our Department between January 2010 and December 2014 we performed a total of 97 pancreaticoduodenectomy. We considered only resectable pancreatic cancer and periampullary neoplasms defined by absence of distant metastases, absence of local tumor extension to the celiac axis and hepatic artery as the lack of involvement of the superior mesenteric vasculature. None of these patients received neoadjuvant chemotherapy. Results: The mean age of these patients was 64.5 years. Jaundice was the commonest presenting symptom associated to anorexia and weight loss. The mean operative time was 295min (±55min). The mean blood loss was 450ml and median blood transfusion was 1 units. 12.1% of patients had an intra-abdominal complication. The commonest complication was Delayed Gastric Emptying responsable of increased length of hospital stay and readmission rate. Postoperative pancreatic fistula of grade C occurred in 4 patients. 2 patients developed a postpancreatectomy hemorrhage. Perioperative mortality was 4.1%. Conclusion: Pancreaticoduodenectomy is a complex surgical technique and the associated high morbidity and mortality resulted in initial reluctance to adopt this surgery for the management of pancreatic and periampullary tumors. Surgical outcomes of pancreatic surgery are better at high-volume experienced center reporting mortality rates below 5%. We perform an end-to-side duct-to-mucosa pancreaticojejunostomy with routinely use of internal pancreatic stent. However no one technique has been shown to definitely be the solution to the problem of postoperative pancreatic fistula. At our center we have a reasonable volume and our data are comparable to literature data