Search for Dark-Matter-Nucleon Interactions via Migdal Effect with DarkSide-50.

Dark matter elastic scattering off nuclei can result in the excitation and ionization of the recoiling atom through the so-called Migdal effect. The energy deposition from the ionization electron adds to the energy deposited by the recoiling nuclear system and allows for the detection of interactions of sub-GeV/c^{2} mass dark matter. We present new constraints for sub-GeV/c^{2} dark matter using the dual-phase liquid argon time projection chamber of the DarkSide-50 experiment with an exposure of (12 306±184) kg d. The analysis is based on the ionization signal alone and significantly enhances the sensitivity of DarkSide-50, enabling sensitivity to dark matter with masses down to 40 MeV/c^{2}. Furthermore, it sets the most stringent upper limit on the spin independent dark matter nucleon cross section for masses below 3.6 GeV/c^{2}.

Search for Dark Matter Particle Interactions with Electron Final States with DarkSide-50.

We present a search for dark matter particles with sub-GeV/c^{2} masses whose interactions have final state electrons using the DarkSide-50 experiment's (12 306±184) kg d low-radioactivity liquid argon exposure. By analyzing the ionization signals, we exclude new parameter space for the dark matter-electron cross section σ[over ¯]_{e}, the axioelectric coupling constant g_{Ae}, and the dark photon kinetic mixing parameter κ. We also set the first dark matter direct-detection constraints on the mixing angle |U_{e4}|^{2} for keV/c^{2} sterile neutrinos.

First Direct Detection Constraints on Planck-Scale Mass Dark Matter with Multiple-Scatter Signatures Using the DEAP-3600 Detector.

Dark matter with Planck-scale mass (≃10^{19} GeV/c^{2}) arises in well-motivated theories and could be produced by several cosmological mechanisms. A search for multiscatter signals from supermassive dark matter was performed with a blind analysis of data collected over a 813 d live time with DEAP-3600, a 3.3 t single-phase liquid argon-based detector at SNOLAB. No candidate signals were observed, leading to the first direct detection constraints on Planck-scale mass dark matter. Leading limits constrain dark matter masses between 8.3×10^{6} and 1.2×10^{19} GeV/c^{2}, and ^{40}Ar-scattering cross sections between 1.0×10^{-23} and 2.4×10^{-18} cm^{2}. These results are interpreted as constraints on composite dark matter models with two different nucleon-to-nuclear cross section scalings.

Pulse-shape discrimination against low-energy Ar-39 beta decays in liquid argon with 4.5 tonne-years of DEAP-3600 data.

The DEAP-3600 detector searches for the scintillation signal from dark matter particles scattering on a 3.3 tonne liquid argon target. The largest background comes from 39 Ar beta decays and is suppressed using pulse-shape discrimination (PSD). We use two types of PSD estimator: the prompt-fraction, which considers the fraction of the scintillation signal in a narrow and a wide time window around the event peak, and the log-likelihood-ratio, which compares the observed photon arrival times to a signal and a background model. We furthermore use two algorithms to determine the number of photons detected at a given time: (1) simply dividing the charge of each PMT pulse by the mean single-photoelectron charge, and (2) a likelihood analysis that considers the probability to detect a certain number of photons at a given time, based on a model for the scintillation pulse shape and for afterpulsing in the light detectors. The prompt-fraction performs approximately as well as the log-likelihood-ratio PSD algorithm if the photon detection times are not biased by detector effects. We explain this result using a model for the information carried by scintillation photons as a function of the time when they are detected.

Differences and Effects of Metabolic Fate of Individual Amino Acid Loss in High-Efficiency Hemodialysis and Hemodiafiltration.

OBJECTIVE: The objective of the study was to quantify the loss and arterial blood concentration of the three main classes of amino acids (AAs)-nonessential amino acids (NEAAs), essential amino acids (EAAs), and branched-chain amino acids-as resulting from high-efficiency hemodialysis (HED) and hemodiafiltration (HDF). We moreover aimed to identify the different fates and metabolic effects manifested in patients undergoing hemodialysis and the consequences on body composition and influence of nutritional decline into protein energy wasting. DESIGN AND METHODS: Identical dialysis monitors, membranes, and dialysate/infusate were used to ensure consistency. Ten patients were recruited and randomized to receive treatment with on-line modern HED and HDF. Arterial plasma concentrations of individual AAs were compared in healthy volunteers and patients undergoing hemodialysis, and AA levels outflowing from the dialyzer were evaluated. Baseline AA plasma levels of patients undergoing hemodialysis were compared with findings obtained 1 year later. RESULTS: A severe loss of AA with HED/HDF was confirmed: a marked loss of total AAs (5 g/session) was detected, corresponding to more than 65% of all AAs. With regard to individual AAs, glutamine displayed a consistent increase (+150%), whereas all other AAs decreased after 12 months of HD/HDF. Only a few AAs, such as proline, cysteine, and histidine maintained normal levels. The most severe metabolic consequences may result from losses of EAAs such as valine, leucine, and histidine and from NEAAs including proline, cysteine, and glutamic acid eliciting the onset of hypercatabolism threatening muscle mass loss. CONCLUSION: Dialysis losses, together with the effect of chronic uremia, resulted in a reduction of fundamental EAAs and NEAAs, which progressively led our patients after 12 months to a deterioration of lean mass toward sarcopenia. Therefore, the reintroduction of a correctly balanced AA supplementation in patients undergoing HD to prevent or halt decline of hypercatabolism into cachexia is recommended.

Development of a shear ultrasonic spectroscopy technique for the evaluation of viscoelastic fluid properties: Theory and experimental validation.

In-situ measurement of viscosity advances the field of rheology, and aides the development of sensing systems for condition and performance monitoring of lubricated mechanisms. Many lubricated mechanisms, such as journal bearings or seals, are characterised by three-layer interfaces; an oil separating two solid (usually metallic) bodies. The viscoelastic study of the lubricating oil in layered systems is possible in-situ by means of ultrasonic reflection (Schirru et al. (2015)). General solutions exist for the reflection of longitudinal plane waves from multi-layered solid-fluid systems. Similar solutions can be applied to plane shear waves. The use of a quarter-wavelength intermediate matching layer improves the sensitivity of the ultrasonic measurement and overcomes problems of acoustic mismatch. This opens the possibility of using reflectance methods to measure engineering (metal-oil) bearing applications that are acoustically mismatched. In this paper, a rigorous mathematical model for wave propagation in a three-layer system is solved for the reflection coefficient modulus and validated using a quarter wavelength ultrasonic viscometer. The model was tested against experimental data for two Newtonian reference fluids, water and hexadecane, and for one non-Newtonian reference fluid, squalene plus polyisoprene (SQL + PIP), measured ultrasonically at frequencies between 5 and 15 MHz. The results are in agreement with the expected viscosity values for the reference fluids. Further, the viscosity measurement is not limited to the resonance frequency, but it is performed over a broad band frequency range. This is important to improve measurement confidence and accurate spectroscopy measurement for the determination of viscoelastic properties.

Constraints on Sub-GeV Dark-Matter-Electron Scattering from the DarkSide-50 Experiment.

We present new constraints on sub-GeV dark-matter particles scattering off electrons based on 6780.0 kg d of data collected with the DarkSide-50 dual-phase argon time projection chamber. This analysis uses electroluminescence signals due to ionized electrons extracted from the liquid argon target. The detector has a very high trigger probability for these signals, allowing for an analysis threshold of three extracted electrons, or approximately 0.05 keVee. We calculate the expected recoil spectra for dark matter-electron scattering in argon and, under the assumption of momentum-independent scattering, improve upon existing limits from XENON10 for dark-matter particles with masses between 30 and 100 MeV/c^{2}.

Low-Mass Dark Matter Search with the DarkSide-50 Experiment.

We present the results of a search for dark matter weakly interacting massive particles (WIMPs) in the mass range below 20 GeV/c^{2} using a target of low-radioactivity argon with a 6786.0 kg d exposure. The data were obtained using the DarkSide-50 apparatus at Laboratori Nazionali del Gran Sasso. The analysis is based on the ionization signal, for which the DarkSide-50 time projection chamber is fully efficient at 0.1 keVee. The observed rate in the detector at 0.5 keVee is about 1.5 event/keVee/kg/d and is almost entirely accounted for by known background sources. We obtain a 90% C.L. exclusion limit above 1.8 GeV/c^{2} for the spin-independent cross section of dark matter WIMPs on nucleons, extending the exclusion region for dark matter below previous limits in the range 1.8-6 GeV/c^{2}.

Average CsI Neutron Density Distribution from COHERENT Data.

Using the coherent elastic neutrino-nucleus scattering data of the COHERENT experiment, we determine for the first time the average neutron rms radius of ^{133}Cs and ^{127}I. We obtain the practically model-independent value R_{n}=5.5_{-1.1}^{+0.9} fm using the symmetrized Fermi and Helm form factors. We also point out that the COHERENT data show a 2.3σ evidence of the nuclear structure suppression of the full coherence.

Laparoscopic limited Heller myotomy without anti-reflux procedure does not induce significant long-term gastroesophageal reflux.

BACKGROUND: Laparoscopic Heller myotomy with partial fundoplication is the gold standard treatment for achalasia. Laparoscopic limited Heller myotomy (LLHM) with no anti-reflux procedure is another possible option. METHODS: A review of prospectively collected data was performed on patients who underwent LLHM from January 1998 to December 2012. Evaluation included gastroscopy, esophageal manometry, 24-h pH-metry, and the Short Form(36) Health Survey(SF-36) questionnaire at baseline and 6 months, as well as the global symptom score at baseline, 6 months, and 5 years post-surgery. Comparison between outcomes was performed with a paired t student's test. RESULTS: 126 patients underwent LLHM. Of these, 60 patients had complete pre and post-operative motility studies. 57 % were female, patient mean age was 45.7 years, with a mean follow-up of 10.53 months. Mean operative time was 56.1 min, and the average length of stay was 1.7 days. At 6 months, a significant decrease in the lower esophageal sphincter resting pressure (29.1 vs. 7.1 mmHg; p < 0.001) and nadir (16.4 vs. 4.3 mmHg; p < 0.001) was observed. Normal esophageal acid exposure (total pH < 4 %) was observed in 68.3 % patients. Nevertheless, of the remaining 31.7 % with abnormal pH-metry, only 21.6 % were clinically symptomatic and all were properly controlled with medical treatment without requiring anti-reflux surgery. Significant improvement in all pre-operative symptoms was observed at 6 months and maintained over 5 years. Dysphagia score was reduced from 9.8 pre-operatively to 2.6 at 5 years (p < 0.001), heartburn score from 3.82 to 2 (p < 0.01), and regurgitation score from 7.5 to 0.8 (p < 0.001). Only one patient (0.8 %) presented with recurrent dysphagia requiring reoperation. CONCLUSION: LLHM without anti-reflux procedure is an effective long-term treatment for achalasia and does not cause symptomatic GERD in three quarters of patients. The remaining patients are well controlled on anti-reflux medications. It is believed that similar clinical results would be obtained during a clinical investigation of the POEM procedure.

Local recurrence and survival after laparoscopic mesorectal resection forrectal adenocarcinoma.

BACKGROUND: Laparoscopic resection for rectal cancer is controversial. Actuarial survival and local recurrence rates have not been determined. METHODS: A prospective database containing 80 consecutive unselected laparoscopic resections of rectal cancers performed between November 1991 and 1999 was reviewed. Local recurrence was defined as any detectable local disease at follow-up assessment occurring either alone or in conjunction with generalized recurrence. The tumor node metastases (TNM) classification for colorectal cancers and the Kaplan-Meier method were used to determine staging and survival curves. The mesorectal excision technique was used during surgery. RESULTS: The median follow-up period was 31 months for patients with stages I, II, and III cancer, and 15.5 months for patients with stage IV cancer. The overall 5-year survival rate was 65.1% for all cancer stages and 72.1% for stages I, II, and III cancer. No trocar-site recurrence was observed. The overall local recurrence rate was 3.75% (3/80) for all cancer stages, and 4.3% (3/70) for stages I, II, and III cancer. CONCLUSIONS: The survival and local recurrence rates for patients with rectal cancer treated by laparoscopic mesorectal excision do not differ negatively from those in the literature for open mesorectal excision. Further validation is needed.

Needlescopic surgery. A logical evolution from conventional laparoscopic surgery.

BACKGROUND: The purpose of this study was to analyze the safety and feasibility of needlescopic surgery and to compare the short-term outcomes relative to conventional laparoscopic surgery. METHODS: Needlescopic surgery patients were compared to matched cohorts of conventional laparoscopic surgery patients from the same prospective database for a variety of selected procedures. RESULTS: A total of 101 needlescopic procedures were analyzed (30 cholecystectomy, 28 Nissen fundoplication, 12 bilateral sympathectomy, 10 splenectomy, 10 Heller myotomy, three adrenalectomy, two colon resection, two splenic cyst excision, four other). There was no significant difference between the needlescopic and conventional laparoscopic groups in conversion rates, morbidity, or mortality. A higher proportion of patients were in hospital

Transperitoneal laparoscopic nephrectomy for giant polycystic kidneys: a case control study.

OBJECTIVES: To describe the technique and compare the surgical outcomes of patients with autosomal dominant polycystic kidney disease (ADPKD) undergoing laparoscopic or open nephrectomy for giant kidneys. METHODS: The surgical outcome of our first 10 consecutive patients with ADPKD who underwent laparoscopic nephrectomy was analyzed from a large prospective computer database. The results were compared with the 10 most recent open nephrectomy procedures performed for ADPKD at the same institution. To facilitate safe laparoscopic hilar dissection, the kidneys were made manageable by volume reduction, accomplished through diligent cyst puncture and aspiration using a novel prototype suction device with a beveled tip. RESULTS: No statistically significant differences were found between the laparoscopic and open surgical groups relative to patient sex, age, or median preoperative kidney size (24.0 versus 21.5 cm, respectively). The laparoscopic patients were significantly heavier than their open counterparts (94 versus 78 kg, P = 0.0095) and had a longer operative time (247 versus 205 minutes, P = 0.04). One conversion to open surgery occurred in the laparoscopic group because cysts were adherent to the spleen and colonic mesentery. No intraoperative complications or deaths occurred in either group and the postoperative complications were similar. The mean length of the postoperative hospitalization was markedly reduced with the laparoscopic compared with the open approach (2.6 versus 6.6 days, P = 0.00002). At a median of 12 months after surgery, none of the laparoscopic patients had recurrent pain, bleeding, or infection. CONCLUSIONS: Laparoscopic nephrectomy is technically safe and feasible in patients with ADPKD. Progressive cyst aspiration is a critical step, facilitating the identification of vital structures and the creation of enough abdominal cavity space to operate. The advantages of this minimally invasive technique include a short hospital stay, minimal pain, low morbidity, and superior cosmesis.

Does a laparoscopic approach to total abdominal colectomy and proctocolectomy offer advantages?

BACKGROUND: Controversy exists regarding the feasibility, safety, and outcomes of laparoscopic total abdominal colectomy (LTAC) and laparoscopic total proctocolectomy (LTPC). The object of this study was to assess the outcomes of LTAC and LTPC and compare them with those of institutional open procedure used as controls. METHODS: Perioperative data and surgical outcomes of patients who underwent TAC or TPC were analyzed and compared retrospectively at a single institution between 1991 and 1999. RESULTS: A total of 73 TACs performed during a 9-year period were evenly distributed between laparoscopic (n = 37) and open (n = 36) approaches. There were no significant differences between patient groups with respect to genders, age, weight, proportion of patients with inflammatory bowel disease, and the number of patients undergoing ileorectal anastomosis. The median operative time was longer with the laparoscopic method (270 vs 178 min; p = 0.001), but the median length of hospital stay was significantly shorter (6 vs 9 days; p = 0.001). The short-term postoperative complication rate up to 30 days from surgery was not statistically different (25% vs 44%; p = 0.137), although there was a clear trend toward a reduced number of overall complications in the laparoscopic group (9 vs 24). Wound complications were significantly fewer (0% vs 19%; p = 0.015) and postoperative pneumonia was nonexistent in laparoscopic patients. Long-term complications also were less common in the laparoscopic group (20% vs 64%; p = 0.002), largely because of reduced incidence of impotence, incisional hernia, and ileostomy complications. Total proctocolectomy was performed laparoscopically in 15 patients and with an open procedure in 13 patients over the same period. There were no statistically significant differences between the two groups with respect to gender, age, weight, and diagnosis. Median operating time was longer for the laparoscopic patients (400 vs 235 min; p = 0.001), whereas the length of hospital stay, morbidity, and mortality were not significantly different. CONCLUSIONS: The results indicate that LTAC can be performed safely with a statistically significant reduction in wound and long-term postoperative complications, as compared with its open counterpart. Operating time is increased, but there is a marked reduction in length of hospital stay. Preliminary results demonstrate that LTPC also is technically feasible and safe, with equal morbidity, mortality, and hospital stay, as compared with open procedures. Studies with larger numbers of patients and a randomized controlled trial giving special attention to patient quality-of-life issues are needed to elucidate the real advantages of this minimally invasive technique.

Laparoscopic colorectal resection in octogenarians.

BACKGROUND: The number and proportion of patients aged ?80 years are increasing. These patients often require surgical care and suffer subsequent high rates of morbidity and mortality. However, the surgical outcomes of laparoscopic colorectal resection in octogenarians are not well documented. METHODS: Octogenarians were identified from a large prospective database comprising 507 consecutive laparoscopic colorectal resections performed between 1991 and 1999 in a university setting. Preoperative comorbidity and surgical outcomes were analyzed. RESULTS: Sixty-two patients (30 men, 32 women) aged ?80 years were identified. Their mean age and weight were 85 years and 63 kg, respectively. Seven patients (11%) were converted to an open procedure. Four (6%) intraoperative complications occurred in four patients (one colon perforation, one small bowel perforation, one burned gallbladder serosa, and one missed lesion), necessitating two conversions. Twenty -four postoperative complications occurred in 19 patients (31%) (six ileus [10%], five wound infections [8%], five cardiac problems [8%], two urinary retentions [3%], two hemorrhages [3%], one abscess [2%], one pneumonia [2%], and two other [3%]). Intraoperative complications did not increase postoperative morbidity. Three patients (5%) died within 30 days of surgery. When the procedure was completed laparoscopically, the overall median postoperative hospital stay was 10.0 days; occurrence of a postoperative complication increased the median length of stay to 15.0 days. CONCLUSIONS: These results are superior to published historical controls involving open colorectal resection in octogenarians. Overall mortality, lung, and urinary tract complications were decreased, and there were no reoperations for small bowel obstruction. Laparoscopic colorectal resection is technically feasible and can be done safely in elderly patients. Results require randomization against those for open surgery to elucida te the real advantages of this technique.

Laparoscopic excision of retroperitoneal tumors: technique and review of the laparoscopic experience.

A technique for laparoscopic excision of benign retroperitoneal tumors, including a teratoma and two cystic lesions, is described. Laparoscopic resection of a 12-cm retroperitoneal teratoma was accomplished with the patient in the left lateral decubitus position. Medial mobilization of the ascending colon and the duodenum was required for access to the lesion. Resections of two cystic lesions (measuring 20 cm and 12 cm) were performed with the patients in the lithotomy position. The colon required medial mobilization in both cases to gain access to the cysts. Once the cysts were dissected from surrounding structures, they were punctured, and the aspirated fluid was sent for cytologic analysis. There were no complications or conversions. Mean operating time was 122 minutes (range, 80-190). Patients were discharged 1 day after surgery, requiring only nonsteroidal anti-inflammatory medications for analgesia. Retroperitoneal tumors can be resected laparoscopically with careful preoperative investigation and meticulous laparoscopic technique. A major advantage of laparoscopic resections is that the patient recovers rapidly with minimal morbidity.

Septic complications of elective laparoscopic colorectal resection.

BACKGROUND: We set out to determine the rate and pattern of septic complications of the surgical wound, abdominal cavity, and urinary and respiratory tracts following laparoscopic colorectal resection. METHODS: A longitudinal database of 500 consecutive cases of colorectal resections was reviewed. RESULTS: The total wound infection rate was 7.2% (36/500) and included infections of the abdominal wall wounds (32/500, 6.4%) and the perineal wounds (4/50, 8%). The anastomotic leak rate in 418 patients who underwent resection with primary anastomosis was 3.3% (14/418). Intraabdominal abscesses were diagnosed in 1% (5/500) of patients. Urinary tract infections were rare (3/500, 0.6%), as was postoperative pneumonia (6/500, 1%). CONCLUSIONS: This study confirms the low rate of postoperative pneumonia observed with all other minimally invasive procedures. Intraabdominal abscesses, urinary tract infections, and postoperative pneumonia occur considerably less frequently than in reported historical controls for open surgery. The rates of abdominal wound infection and anastomotic leak in laparoscopic colorectal resection appear to be equivalent to traditional surgery, whereas the rate of perineal wound sepsis is lower. Comparative studies are needed to determine the differential costs of the septic episodes associated with the two approaches.

Defining a learning curve for laparoscopic colorectal resections.

PURPOSE: The purpose of this review was to define the learning curve for laparoscopic colorectal resections. METHODS: A prospectively accumulated, computerized database of all laparoscopic colorectal resections performed by three surgeons between April 1991 and March 1999 was reviewed. RESULTS: A total of 461 consecutive resections were evenly distributed among three surgeons (141, 155, and 165). Median operating time was 180 minutes for Cases 1 to 30 in each surgeon's experience and declined to a steady state (150-167.5 minutes) for Cases 31 and higher. Subsequently, Cases 1 to 30 were considered "early experience," whereas Cases 31 and higher were combined as "late experience" for statistical analysis. There were no significant differences between patients undergoing resections in the early experience and those undergoing resections in the late experience with respect to age, weight, or proportion of patients with malignancy, diverticulitis, or inflammatory bowel disease. There were greater proportions of males (42 vs. 54 percent, P = 0.046) and rectal resections performed (14 vs. 32 percent, P = 0.002) in the late experience. Trends toward declining rates of intraoperative complications (9 vs. 7 percent, P = 0.70) and conversion to open surgery (13.5 vs. 9.7 percent, P = 0.39) were observed with experience. Median operating time (180 vs. 160 minutes, P < 0.001) and overall length of postoperative hospital stay (6.5 vs. 5 days, P < 0.001) declined significantly with experience. There was no difference in the rate of postoperative complications between early and late experience (30 vs. 32 percent, P = 0.827). CONCLUSIONS: The learning curve for performing colorectal resections was approximately 30 procedures in this study, based on a decline in operating time, intraoperative complications, and conversion rate. Learning was also extended to clinical care because it was appreciated that patients could be discharged to their homes more quickly.