GW170817: Implications for the Stochastic Gravitational-Wave Background from Compact Binary Coalescences

The LIGO Scientific and Virgo Collaborations have announced the event GW170817, the first detection of gravitational waves from the coalescence of two neutron stars. The merger rate of binary neutron stars estimated from this event suggests that distant, unresolvable binary neutron stars create a significant astrophysical stochastic gravitational-wave background. The binary neutron star component will add to the contribution from binary black holes, increasing the amplitude of the total astrophysical background relative to previous expectations. In the Advanced LIGO-Virgo frequency band most sensitive to stochastic backgrounds (near 25 Hz), we predict a total astrophysical background with amplitude Ω_{GW}(f=25  Hz)=1.8_{-1.3}^{+2.7}×10^{-9} with 90% confidence, compared with Ω_{GW}(f=25  Hz)=1.1_{-0.7}^{+1.2}×10^{-9} from binary black holes alone. Assuming the most probable rate for compact binary mergers, we find that the total background may be detectable with a signal-to-noise-ratio of 3 after 40 months of total observation time, based on the expected timeline for Advanced LIGO and Virgo to reach their design sensitivity.

Looking beyond drivers and passengers in cancer genome sequencing data

Cancer arises as a result of acquired changes in the DNA sequence of the genome of somatic cells. A subset of the genetic changes, dubbed driver mutations, propels tumor growth, and the remaining changes are passengers, apparently inconsequential for neoplastic transformation. Massive genome sequencing of thousands of tumors from all major cancer types has enabled cataloging of the so-called driver and passenger mutations, and facilitated molecular classification of cancer, guiding precision medicine approach for the patients. Nonetheless, innovative analyses of cancer genomics data has led to novel, sometimes serendipitous findings that have aided to our understanding of other aspects of the biology of the disease and opened up new frontiers. For instance, emerging findings show that mutational patterns in cancer genomes can help detect signatures of known and novel DNA damage and repair processes, provide a likely chronological account of genomic changes in cancer genomes, and allow revisiting the models of cancer evolution. These findings have stimulated original approaches to identify disease etiology, stratify patients, target the disease, and monitor patient responses, complementing driver-mutation centric approaches. In this review, we discuss these emerging approaches and unexpected breakthroughs, and their implications for basic cancer research and clinical practices.

FUSE certification enhances performance on a virtual computer based simulator for dispersive electrode placement

BACKGROUND

The Society of American Gastrointestinal and Endoscopic Surgeons (SAGES) has developed the fundamental use of surgical energy (FUSE) didactic curriculum in order to further understanding of the safe use of surgical energy. The virtual electrosurgical skill trainer (VEST) is being developed as a complementary simulation-based curriculum, with several modules already existing. Subsequently, a new VEST module has been developed about dispersive electrode placement. The purpose of this study is to assess knowledge about dispersive electrode placement in surgeons and surgical trainees in addition to describing a new VEST module.

METHODS

Forty-six subjects (n = 46) were recruited for participation at the 2016 SAGES conference Learning Center. Subjects were asked to complete demographic surveys, a five-question pre-test, and a five-question post-test after completing the VEST dispersive electrode module. Subjects were then asked to rate different aspects of the module using a five-point Likert scale questionnaire.

RESULTS

Mean pre-simulator and post-simulator assessment scores were 1.5 and 3.4, respectively, with Wilcoxon signed rank analysis showing a significant difference in the means (p < 0.05). Subjects were grouped by the presence (n = 12) or absence (n = 31) of prior FUSE experience and by training level. Mann-Whitney U testing showed no significant difference in pre-simulator assessment scores between attending surgeons and trainees (p > 0.05). In those with and without FUSE exposure, a significant difference (p < 0.05) was seen in pre-simulator assessment scores, and no significant difference in Likert scale assessment scores was seen.

CONCLUSIONS

This study demonstrated a new VEST educational module. Consistently high Likert assessment scores showed that users felt that the VEST module helped their understanding of dispersive electrode placement. Additionally, the study reflected a potential knowledge deficit in the safe use of dispersive electrodes in the surgical community, also demonstrating that even some exposure to the FUSE curriculum developed by SAGES provides increased awareness about dispersive electrode use.

Immersive virtual reality-based training improves response in a simulated operating room fire scenario

BACKGROUND

SAGES FUSE curriculum provides didactic knowledge on OR fire prevention. The objective of this study is to evaluate the impact of an immersive virtual reality (VR)-based OR fire training simulation system in combination with FUSE didactics.

METHODS

The study compared a control with a simulation group. After a pre-test questionnaire that assessed the baseline knowledge, both groups were given didactic material that consists of a 10-min presentation and reading materials about precautions and stopping an OR fire from the FUSE manual. The simulation group practiced on the OR fire simulation for one session that consisted of five trials within a week from the pre-test. One week later, both groups were reassessed using a questionnaire. A week after the post-test both groups also participated in a simulated OR fire scenario while their performance was videotaped for assessment.

RESULTS

A total of 20 subjects (ten per group) participated in this IRB approved study. Median test scores for the control group increased from 5.5 to 9.00 (p = 0.011) and for the simulation group it increased from 5.0 to 8.5 (p = 0.005). Both groups started at the same baseline (pre-test, p = 0.529) and reached similar level in cognitive knowledge (post-test, p = 0.853). However, when tested in the mock OR fire scenario, 70% of the simulation group subjects were able to perform the correct sequence of steps in extinguishing the simulated fire whereas only 20% subjects in the control group were able to do so (p = 0.003). The simulation group was better than control group in correctly identifying the oxidizer (p = 0.03) and ignition source (p = 0.014).

CONCLUSIONS

Interactive VR-based hands-on training was found to be a relatively inexpensive and effective mode for teaching OR fire prevention and management scenarios.

First Search for Nontensorial Gravitational Waves from Known Pulsars

We present results from the first directed search for nontensorial gravitational waves. While general relativity allows for tensorial (plus and cross) modes only, a generic metric theory may, in principle, predict waves with up to six different polarizations. This analysis is sensitive to continuous signals of scalar, vector, or tensor polarizations, and does not rely on any specific theory of gravity. After searching data from the first observation run of the advanced LIGO detectors for signals at twice the rotational frequency of 200 known pulsars, we find no evidence of gravitational waves of any polarization. We report the first upper limits for scalar and vector strains, finding values comparable in magnitude to previously published limits for tensor strain. Our results may be translated into constraints on specific alternative theories of gravity.

179 Xenogeneic and Allogeneic Mesenchymal Stem Cell Transplantation for Treatment of Tibial Bone Fracture in Mice

Among stem cells, mesenchymal stem cells (MSC) are best suited for therapeutic purposes because of their immunomodulatory properties, ability to be isolated from adult animal at any stage, ease of propagation in the laboratory, and so on. The present study was carried out to isolate and characterise MSC from adipose tissue of mouse (Mus musculus), and to test their application for the treatment of fractured tibia bone in mouse. Cattle and buffalo MSC, already cultured and characterised in our laboratory, were used in the present study as xenogeneic MSC to observe the healing in mouse model. Murine Ad-MSC were isolated from mouse inguinal fat pad by enzymatic digestion method and cultured in growth enriching medium in standard culture conditions. To test the therapeutic potential of MSC, 24 mice were divided into 4 groups: control (C), allogeneic (A), cattle xenogeneic (CX), and buffalo xenogeneic (BX) with 6 mice (having tibial bone mechanical fractured) in each group, and had the corresponding MSC cells injected in the fracture area. The control group was not subjected to any kind of MSC treatment. Post-treatment, healing in all groups was examined for 36 days at different intervals (Days 1, 12, 24, and 36) via digital X-ray imaging. A bone healing score was assigned to each mouse per the protocol provided by RUST (Radiographic Union Scale in Tibial bone) fractures. The results of present study showed that murine Ad-MSC were positive for MSC-specific markers CD44, CD90, CD105, and negative for CD34 and CD45 via RT-PCR and immunocytochemistry. The Ad-MSC were also positive for the alkaline phosphatase staining. Statistical analysis, using Proc GLM (SAS Institute Inc., Cary, NC, USA), revealed that the bone healing was significantly different (P < 0.01) between group C (1.708 ± 0.059) and other groups [group A (2.125 ± 0.061), CX (2.167 ± 0.068), BX (2.250 ± 0.068)], suggesting that healing was greater in groups transplanted with MSC compared with control. However, healing between groups transplanted with MSC (A, CX, and BX) was not significantly different (P > 0.05). In conclusion, we have observed the healing potential of MSC in mouse model via allogeneic and xenogeneic MSC transplantation; the healing potential among the A, CX, and BX MSC groups was similar.

Prospects for observing and localizing gravitational-wave transients with Advanced LIGO, Advanced Virgo and KAGRA

We present possible observing scenarios for the Advanced LIGO, Advanced Virgo and KAGRA gravitational-wave detectors over the next decade, with the intention of providing information to the astronomy community to facilitate planning for multi-messenger astronomy with gravitational waves. We estimate the sensitivity of the network to transient gravitational-wave signals, and study the capability of the network to determine the sky location of the source. We report our findings for gravitational-wave transients, with particular focus on gravitational-wave signals from the inspiral of binary neutron star systems, which are the most promising targets for multi-messenger astronomy. The ability to localize the sources of the detected signals depends on the geographical distribution of the detectors and their relative sensitivity, and [Formula: see text] credible regions can be as large as thousands of square degrees when only two sensitive detectors are operational. Determining the sky position of a significant fraction of detected signals to areas of 5-[Formula: see text] requires at least three detectors of sensitivity within a factor of [Formula: see text] of each other and with a broad frequency bandwidth. When all detectors, including KAGRA and the third LIGO detector in India, reach design sensitivity, a significant fraction of gravitational-wave signals will be localized to a few square degrees by gravitational-wave observations alone.

J/ψ Elliptic Flow in Pb-Pb Collisions at sqrt[s_{NN}]=5.02 TeV

We report a precise measurement of the J/ψ elliptic flow in Pb-Pb collisions at sqrt[s_{NN}]=5.02  TeV with the ALICE detector at the LHC. The J/ψ mesons are reconstructed at midrapidity (|y|<0.9) in the dielectron decay channel and at forward rapidity (2.5<y<4.0) in the dimuon channel, both down to zero transverse momentum. At forward rapidity, the elliptic flow v_{2} of the J/ψ is studied as a function of the transverse momentum and centrality. A positive v_{2} is observed in the transverse momentum range 2<p_{T}<8  GeV/c in the three centrality classes studied and confirms with higher statistics our earlier results at sqrt[s_{NN}]=2.76  TeV in semicentral collisions. At midrapidity, the J/ψ  v_{2} is investigated as a function of the transverse momentum in semicentral collisions and found to be in agreement with the measurements at forward rapidity. These results are compared to transport model calculations. The comparison supports the idea that at low p_{T} the elliptic flow of the J/ψ originates from the thermalization of charm quarks in the deconfined medium but suggests that additional mechanisms might be missing in the models.

Viscoelastic flow past mono- and bidisperse random arrays of cylinders: flow resistance, topology and normal stress distribution

We investigate creeping viscoelastic fluid flow through two-dimensional porous media consisting of random arrangements of monodisperse and bidisperse cylinders, using our finite volume-immersed boundary method introduced in S. De, et al., J. Non-Newtonian Fluid Mech., 2016, 232, 67-76. The viscoelastic fluid is modeled with a FENE-P model. The simulations show an increased flow resistance with increase in flow rate, even though the bulk response of the fluid to shear flow is shear thinning. We show that if the square root of the permeability is chosen as the characteristic length scale in the determination of the dimensionless Deborah number (De), then all flow resistance curves collapse to a single master curve, irrespective of the pore geometry. Our study reveals how viscoelastic stresses and flow topologies (rotation, shear and extension) are distributed through the porous media, and how they evolve with increasing De. We correlate the local viscoelastic first normal stress differences with the local flow topology and show that the largest normal stress differences are located in shear flow dominated regions and not in extensional flow dominated regions at higher viscoelasticity. The study shows that normal stress differences in shear flow regions may play a crucial role in the increase of flow resistance for viscoelastic flow through such porous media.

In Situ Mechanical Characterization of Multilayer Soft Tissue Using Ultrasound Imaging

In this paper, we report the development of a technique to characterize layer-specific nonlinear material properties of soft tissue in situ with the potential for in vivo testing. A soft tissue elastography robotic arm system comprising of a robotically manipulated 30 MHz high-resolution ultrasound probe, a custom designed compression head, and load cells has been developed to perform compression ultrasound imaging on the target tissue and measure reaction forces. A multilayer finite element model is iteratively optimized to identify the material coefficients of each layer. Validation has been performed using tissue mimicking agar-based phantoms with a low relative error of ∼7% for two-layer phantoms and ∼10% error for three layer phantoms when compared to known ground-truth values obtained using a commercial material testing system. The technique has then been used to successfully determine the in situ layer-specific mechanical properties of intact porcine stomach. The mean C10 and C20 for a second-order reduced polynomial material model were determined for the muscularis (6.41 ± 0.60, 4.29 ± 1.87 kPa), submucosal (5.21 ± 0.57, 3.68 ± 3.01 kPa), and mucosal layers (0.06 ± 0.02, 0.09 ± 0.24 kPa). Such a system can be utilized to perform in vivo mechanical characterization, which is left as future work.

Virtual interactive suturing for the Fundamentals of Laparoscopic Surgery (FLS)

BACKGROUND

Suturing with intracorporeal knot-tying is one of the five tasks of the Fundamentals of Laparoscopic Surgery (FLS), which is a pre-requisite for board certification in general surgery. This task involves placing a short suture through two marks in a penrose drain and then tying a double-throw knot followed by two single-throw knots using two needle graspers operated by both hands. A virtual basic laparoscopic skill trainer (VBLaST©) is being developed to represent the virtual versions of the FLS tasks, including automated, real time performance measurement and feedback. In this paper, we present the development of a VBLaST suturing simulator (VBLaST-SS©). Developing such a simulator involves solving multiple challenges associated with fast collision detection, response and force feedback.

METHODS

In this paper, we present a novel projection-intersection based knot detection method, which can identify the validity of different types of knots at haptic update rates. A simple and robust edge-edge based collision detection algorithm is introduced to support interactive knot tying and needle insertion operations. A bimanual hardware interface integrates actual surgical instruments with haptic devices enabling not only interactive rendering of force feedback but also realistic sensation of needle grasping, which realizes an immersive surgical suturing environment.

RESULTS

Experiments on performing the FLS intracorporeal suturing task show that the simulator is able to run on a standard personal computer at interactive rates.

CONCLUSIONS

VBLaST-SS© is a computer-based interactive virtual simulation system for FLS intracorporeal knot-tying suturing task that can provide real-time objective assessment for the user's performance.

GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral

On August 17, 2017 at 12∶41:04 UTC the Advanced LIGO and Advanced Virgo gravitational-wave detectors made their first observation of a binary neutron star inspiral. The signal, GW170817, was detected with a combined signal-to-noise ratio of 32.4 and a false-alarm-rate estimate of less than one per 8.0×10^{4}  years. We infer the component masses of the binary to be between 0.86 and 2.26  M_{⊙}, in agreement with masses of known neutron stars. Restricting the component spins to the range inferred in binary neutron stars, we find the component masses to be in the range 1.17-1.60  M_{⊙}, with the total mass of the system 2.74_{-0.01}^{+0.04}M_{⊙}. The source was localized within a sky region of 28  deg^{2} (90% probability) and had a luminosity distance of 40_{-14}^{+8}  Mpc, the closest and most precisely localized gravitational-wave signal yet. The association with the γ-ray burst GRB 170817A, detected by Fermi-GBM 1.7 s after the coalescence, corroborates the hypothesis of a neutron star merger and provides the first direct evidence of a link between these mergers and short γ-ray bursts. Subsequent identification of transient counterparts across the electromagnetic spectrum in the same location further supports the interpretation of this event as a neutron star merger. This unprecedented joint gravitational and electromagnetic observation provides insight into astrophysics, dense matter, gravitation, and cosmology.

Validation of the VBLaST pattern cutting task: a learning curve study

BACKGROUND

Mastery of laparoscopic skills is essential in surgical practice and requires considerable time and effort to achieve. The Virtual Basic Laparoscopic Skill Trainer (VBLaST-PC^©) is a virtual simulator that was developed as a computerized version of the pattern cutting (PC) task in the Fundamentals of Laparoscopic Surgery (FLS) system. To establish convergent validity for the VBLaST-PC^©, we assessed trainees' learning curves using the cumulative summation (CUSUM) method and compared them with those on the FLS.

METHODS

Twenty-four medical students were randomly assigned to an FLS training group, a VBLaST training group, or a control group. Fifteen training sessions, 30 min in duration per session per day, were conducted over 3 weeks. All subjects completed pretest, posttest, and retention test (2 weeks after posttest) on both the FLS and VBLaST^© simulators. Performance data, including time, error, FLS score, learning rate, learning plateau, and CUSUM score, were analyzed.

RESULTS

The learning curve for all trained subjects demonstrated increasing performance and a performance plateau. CUSUM analyses showed that five of the seven subjects reached the intermediate proficiency level but none reached the expert proficiency level after 150 practice trials. Performance was significantly improved after simulation training, but only in the assigned simulator. No significant decay of skills after 2 weeks of disuse was observed. Control subjects did not show any learning on the FLS simulator, but improved continually in the VBLaST simulator.

CONCLUSIONS

Although VBLaST^©- and FLS-trained subjects demonstrated similar learning rates and plateaus, the majority of subjects required more than 150 trials to achieve proficiency. Trained subjects demonstrated improved performance in only the assigned simulator, indicating specificity of training. The virtual simulator may provide better opportunities for learning, especially with limited training exposure.

GW170814: A Three-Detector Observation of Gravitational Waves from a Binary Black Hole Coalescence

On August 14, 2017 at 10∶30:43 UTC, the Advanced Virgo detector and the two Advanced LIGO detectors coherently observed a transient gravitational-wave signal produced by the coalescence of two stellar mass black holes, with a false-alarm rate of ≲1 in 27 000 years. The signal was observed with a three-detector network matched-filter signal-to-noise ratio of 18. The inferred masses of the initial black holes are 30.5_{-3.0}^{+5.7}M_{⊙} and 25.3_{-4.2}^{+2.8}M_{⊙} (at the 90% credible level). The luminosity distance of the source is 540_{-210}^{+130}  Mpc, corresponding to a redshift of z=0.11_{-0.04}^{+0.03}. A network of three detectors improves the sky localization of the source, reducing the area of the 90% credible region from 1160   deg^{2} using only the two LIGO detectors to 60  deg^{2} using all three detectors. For the first time, we can test the nature of gravitational-wave polarizations from the antenna response of the LIGO-Virgo network, thus enabling a new class of phenomenological tests of gravity.

Anomalous Evolution of the Near-Side Jet Peak Shape in Pb-Pb Collisions at sqrt[s_{NN}]=2.76 TeV

The measurement of two-particle angular correlations is a powerful tool to study jet quenching in a p_{T} region inaccessible by direct jet identification. In these measurements pseudorapidity (Δη) and azimuthal (Δφ) differences are used to extract the shape of the near-side peak formed by particles associated with a higher p_{T} trigger particle (1<p_{T,trig}<8  GeV/c). A combined fit of the near-side peak and long-range correlations is applied to the data allowing the extraction of the centrality evolution of the peak shape in Pb-Pb collisions at sqrt[s_{NN}]=2.76  TeV. A significant broadening of the peak in the Δη direction at low p_{T} is found from peripheral to central collisions, which vanishes above 4  GeV/c, while in the Δφ direction the peak is almost independent of centrality. For the 10% most central collisions and 1<p_{T,assoc}<2  GeV/c, 1<p_{T,trig}<3  GeV/c a novel feature is observed: a depletion develops around the center of the peak. The results are compared to pp collisions at the same center of mass energy and ampt model simulations. The comparison to the investigated models suggests that the broadening and the development of the depletion is connected to the strength of radial and longitudinal flow.

OR fire virtual training simulator: design and face validity

BACKGROUND

The Virtual Electrosurgical Skill Trainer is a tool for training surgeons the safe operation of electrosurgery tools in both open and minimally invasive surgery. This training includes a dedicated team-training module that focuses on operating room (OR) fire prevention and response. The module was developed to allow trainees, practicing surgeons, anesthesiologist, and nurses to interact with a virtual OR environment, which includes anesthesia apparatus, electrosurgical equipment, a virtual patient, and a fire extinguisher. Wearing a head-mounted display, participants must correctly identify the "fire triangle" elements and then successfully contain an OR fire. Within these virtual reality scenarios, trainees learn to react appropriately to the simulated emergency. A study targeted at establishing the face validity of the virtual OR fire simulator was undertaken at the 2015 Society of American Gastrointestinal and Endoscopic Surgeons conference.

METHODS

Forty-nine subjects with varying experience participated in this Institutional Review Board-approved study. The subjects were asked to complete the OR fire training/prevention sequence in the VEST simulator. Subjects were then asked to answer a subjective preference questionnaire consisting of sixteen questions, focused on the usefulness and fidelity of the simulator.

RESULTS

On a 5-point scale, 12 of 13 questions were rated at a mean of 3 or greater (92%). Five questions were rated above 4 (38%), particularly those focusing on the simulator effectiveness and its usefulness in OR fire safety training. A total of 33 of the 49 participants (67%) chose the virtual OR fire trainer over the traditional training methods such as a textbook or an animal model.

CONCLUSIONS

Training for OR fire emergencies in fully immersive VR environments, such as the VEST trainer, may be the ideal training modality. The face validity of the OR fire training module of the VEST simulator was successfully established on many aspects of the simulation.

Convergent validation and transfer of learning studies of a virtual reality-based pattern cutting simulator

INTRODUCTION

Research has clearly shown the benefits of surgical simulators to train laparoscopic motor skills required for positive patient outcomes. We have developed the Virtual Basic Laparoscopic Skill Trainer (VBLaST) that simulates tasks from the Fundamentals of Laparoscopic Surgery (FLS) curriculum. This study aims to show convergent validity of the VBLaST pattern cutting module via the CUSUM method to quantify learning curves along with motor skill transfer from simulation environments to ex vivo tissue samples.

METHODS

18 medical students at the University at Buffalo, with no prior laparoscopic surgical skills, were placed into the control, FLS training, or VBLaST training groups. Each training group performed pattern cutting trials for 12 consecutive days on their respective simulation trainers. Following a 2-week break period, the trained students performed three pattern cutting trials on each simulation platform to measure skill retention. All subjects then performed one pattern cutting task on ex vivo cadaveric peritoneal tissue. FLS and VBLaST pattern cutting scores, CUSUM scores, and transfer task completion times were reported.

RESULTS

Results indicate that the FLS and VBLaST trained groups have significantly higher task performance scores than the control group in both the VBLaST and FLS environments (p < 0.05). Learning curve results indicate that three out of seven FLS training subjects and four out of six VBLaST training subjects achieved the "senior" performance level. Furthermore, both the FLS and VBLaST trained groups had significantly lower transfer task completion times on ex vivo peritoneal tissue models (p < 0.05).

CONCLUSION

We characterized task performance scores for trained VBLaST and FLS subjects via CUSUM analysis of the learning curves and showed evidence that both groups have significant improvements in surgical motor skill. Furthermore, we showed that learned surgical skills in the FLS and VBLaST environments transfer not only to the different simulation environments, but also to ex vivo tissue models.

Thermal injury of skin and subcutaneous tissues: A review of experimental approaches and numerical models

Thermal injury to skin and subcutaneous tissue is common in both civilian and combat scenarios. Understanding the change in tissue morphologies and properties and the underlying mechanisms of thermal injury are of vital importance to clinical determination of the degree of burn and treatment approach. This review aims at summarizing the research involving experimental and numerical studies of skin and subcutaneous tissue subjected to thermal injury. The review consists of two parts. The first part deals with experimental studies including burn protocols and prevailing imaging approaches. The second part deals with existing numerical models for burns of tissue and related computational simulations. Based on this review, we conclude that though there is literature contributing to the knowledge of the pathology and pathogenesis of tissue burn, there is scant quantitative information regarding changes in tissue properties including mechanical, thermal, electrical and optical properties as a result of burns that are linked to altered tissue morphology.