Two-photon rubidium clock detecting 776 nm fluorescence.

The optical atomic clock based on the 5S1/2 → 5D5/2 two-photon transition in rubidium is a candidate for a next generation, manufacturable, portable clock that fits in a small size, weight, and power (SWaP) envelope. Here, we report the first two-photon rubidium clock stabilized by detecting 776 nm fluorescence. We also demonstrate the use of a multi-pixel photon counter as a low voltage substitute to a photomultiplier tube in the feedback loop to the clock laser.

Measurement of Optical Rubidium Clock Frequency Spanning 65 Days.

Optical clocks are emerging as next-generation timekeeping devices with technological and scientific use cases. Simplified atomic sources such as vapor cells may offer a straightforward path to field use, but suffer from long-term frequency drifts and environmental sensitivities. Here, we measure a laboratory optical clock based on warm rubidium atoms and find low levels of drift on the month-long timescale. We observe and quantify helium contamination inside the glass vapor cell by gradually removing the helium via a vacuum apparatus. We quantify a drift rate of 4×10-15/day, a 10 day Allan deviation less than 5×10-15, and an absolute frequency of the Rb-87 two-photon clock transition of 385,284,566,371,190(1970) Hz. These results support the premise that optical vapor cell clocks will be able to meet future technology needs in navigation and communications as sensors of time and frequency.

Ability to Perform Laparoscopic Intra- and Extracorporeal Suture Ligations in a Live Canine Ovariectomy Model after Simulation Training.

Veterinary resident training in minimally invasive surgery is currently inconsistent and depends on innate psychomotor skills. Simulation training has been shown to effectively increase basic skills, but demonstration of simulation training effects on advanced skills in the operating room is sparse. We aimed to determine if simulation-trained novice surgeons were able to perform laparoscopic suture ligation in live dogs. Three novice laparoscopic surgeons underwent a 12-session simulation training program with subsequent laparoscopic skills testing to demonstrate competency. The median skills scores of trainees and of one experienced surgeon were 417 and 472, respectively. Eighteen healthy client-owned (shelter) dogs were operated on by four surgeons: one experienced American College of Veterinary Surgeons (ACVS) diplomate, two novice ACVS residents, and one novice ACVS diplomate. Laparoscopic ovariectomy was performed with suture ligation of the ovarian pedicles. Successful surgery was defined as no evidence of ovarian vessel bleeding after transection of the pedicles. Simulation-trained novices performed successful suture-ligated ovariectomies in 11/13 dogs (85%), and the experienced surgeon in 5/5 (100%) dogs. Median total ligation time was 30 minutes (range: 17-57), which was not different among surgeons (p = .118). Median total surgery time was 105 minutes (range: 69-156) for novices and 89 minutes (range: 65-99) for the experienced surgeon (p = .038). Extensive simulation training including suturing may contribute toward surgery residents being able to perform complex laparoscopic procedures. These results need to be confirmed in larger numbers of trainees.

Chaperone Nap1 shields histone surfaces used in a nucleosome and can put H2A-H2B in an unconventional tetrameric form.

The histone H2A-H2B heterodimer is an integral component of the nucleosome. The cellular localization and deposition of H2A-H2B into chromatin is regulated by numerous factors, including histone chaperones such as nucleosome assembly protein 1 (Nap1). We use hydrogen-deuterium exchange coupled to mass spectrometry to characterize H2A-H2B and Nap1. Unexpectedly, we find that at low ionic strength, the α helices in H2A-H2B are frequently sampling partially disordered conformations and that binding to Nap1 reduces this conformational sampling. We identify the interaction surface between H2A-H2B and Nap1 and confirm its relevance both in vitro and in vivo. We show that two copies of H2A-H2B bound to a Nap1 homodimer form a tetramer with contacts between H2B chains similar to those in the four-helix bundle structural motif. The organization of the complex reveals that Nap1 competes with histone-DNA and interhistone interactions observed in the nucleosome, thereby regulating the availability of histones for chromatin assembly.

Comparison between intracorporeal and extracorporeal ligations in a laparoscopic ovariectomy model in dogs.

OBJECTIVE: To compare the influence of extracorporeal and intracorporeal ligations on the duration of and complications associated with laparoscopic ovariectomy in dogs. STUDY DESIGN: Prospective randomized experimental study. ANIMALS: Healthy intact female dogs (n = 18). METHODS: The left and right ovarian pedicles of dogs undergoing laparoscopic ovariectomy were randomly assigned to intracorporeal (n = 18) or extracorporeal (n = 18) ligation groups. Surgeries were performed by two American College of Veterinary Surgeons (ACVS) diplomates and two ACVS residents. The time required to place extracorporeal and intracorporeal ligations, duration of surgery, and intraoperative complications were compared between ligation techniques. Postoperative complications were recorded. RESULTS: The time required for intracorporeal ligation (17.3 ± 8.7 minutes) did not differ from that required for extracorporeal ligation (15.1 ± 6.1 minutes; P = .38). The total duration of surgery was 102.7 ± 28.7 minutes including portal placement and veterinary student closure of incisions. Ligation of the ovarian pedicle was successful in 16 of 17 dogs. Intraoperative hemorrhage occurred in three dogs, and postoperative complications were noted in three dogs, without apparent difference between ligation techniques. CONCLUSION: No difference was identified between extracorporeal and intracorporeal ligations of ovarian pedicles. CLINICAL SIGNIFICANCE: This study does not provide evidence to support one ligation technique rather than the other.

The method of attachment influences accelerometer-based activity data in dogs.

BACKGROUND: Accelerometer-based activity monitoring is a promising new tool in veterinary medicine used to objectively assess activity levels in dogs. To date, it is unknown how device orientation, attachment method, and attachment of a leash to the collar holding an accelerometer affect canine activity data. It was our goal to evaluate whether attachment methods of accelerometers affect activity counts. Eight healthy, client-owned dogs were fitted with two identical neck collars to which two identical activity monitors were attached using six different methods of attachment. These methods of attachment evaluated the use of a protective case, positioning of the activity monitor and the tightness of attachment of the accelerometer. Lastly, the effect of leash attachment to the collar was evaluated. For trials where the effect of leash attachment to the collar was not being studied, the leash was attached to a harness. Activity data obtained from separate monitors within a given experiment were compared using Pearson correlation coefficients and across all experiments using the Kruskal-Wallis Test. RESULTS: There was excellent correlation and low variability between activity monitors on separate collars when the leash was attached to a harness, regardless of their relative positions. There was good correlation when activity monitors were placed on the same collar regardless of orientation. There were poor correlations between activity monitors in three experiments: when the leash was fastened to the collar that held an activity monitor, when one activity monitor was housed in the protective casing, and when one activity monitor was loosely zip-tied to the collar rather than threaded on using the provided metal loop. Follow-up, pair-wise comparisons identified the correlation associated with these three methods of attachment to be statistically different from the level of correlation when monitors were placed on separate collars. CONCLUSIONS: While accelerometer-based activity monitors are useful tools to objectively assess physical activity in dogs, care must be taken when choosing a method to attach the device. The attachment of the activity monitor to the collar should utilize a second, dedicated collar that is not used for leash attachment and the attachment method should remain consistent throughout a study period.

Arthroscopic-Assisted Toggle Rod Stabilization in Canine Coxofemoral Luxation: A Cadaveric Study.

OBJECTIVE: The aim of this study was to describe an arthroscopic-assisted technique for coxofemoral toggle rod placement, and to report on the feasibility, drill tunnel trajectory and accuracy of tunnel aperture location using this method. STUDY DESIGN: Cadaveric pilot study. SAMPLE POPULATION: Eight coxofemoral joints. METHODS: Craniodorsal coxofemoral joint luxations were artificially created. A simulated open hip reduction and stabilization with a toggle rod were performed through a limited arthrotomy under arthroscopic guidance. Computed tomography scans were performed to evaluate drill hole trajectory across the femoral neck, and joints were disarticulated and photographed. Digital imaging software was used to determine the percent overlap of the drill hole apertures relative to the origin and insertion of the round ligament on the acetabulum and fovea. RESULTS: The exit point of the tunnel was entirely within the fovea capitis in five of eight femurs, three of eight femoral drill apertures were only partially within the target area. Of the eight acetabular bone tunnels examined, all were centred occupying the acetabular fossa. CONCLUSIONS: Coxofemoral toggle rod placement can be performed under arthroscopic guidance through a limited arthrotomy. Comparable femoral tunnel accuracy with the standard open technique should be achieved with the current method prior to its clinical use.