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A new mathematical model is presented to describe both the active and passive mechanics of muscles. In order to account for the active response, a two–layer kinematics that introduces both the visible and rest lengths of the muscle is presented within a rational mechanics framework. The formulation is based on an extended version of the principle of virtual power and the dissipation principle. By using an accurate constitutive description of muscle mobility under activation, details of microscopic processes that lead to muscle contraction are glossed over while macroscopic effects of chemical/electrical stimuli on muscle mechanics are retained. The model predictions are tested with isometric and isotonic experimental data collected from murine extensor digitorum muscle. It is shown that the proposed model captures experimental observations with only three scalar parameters. [ABSTRACT FROM AUTHOR]

A novel continuum model is proposed to describe the deformations of a planar lipid bilayer suspended across a circular pore. The model is derived within a new theoretical framework for smectic A liquid crystals in which the usual director n , which defines the average orientation of the molecules, is not constrained to be normal to the layers. The free energy is defined by considering the elastic splay of the director, the bending and compression of the lipid bilayer, the cost of tilting the director with respect to the layer normal, the surface tension, and the weak anchoring of the director. Variational methods are used to derive the equilibrium equations and boundary conditions. The resulting boundary value problem is then solved numerically to compute the fully nonlinear displacement of the layers and tilt of the lipid molecules. A parametric study shows that an increase in surface tension produces a decrease in the deformation of the lipid bilayers while an opposite effect is obtained when increasing the anchoring strength. [ABSTRACT FROM AUTHOR]

Abstract: The security of ports and transportation is of utmost importance for the development of economy and the security of a nation. Among the necessary actions to ensure the security of ports and borders, the inspection of containers is one of the most time consuming and expensive procedures. Potential threats are the illegal traffic of radioactive materials that could be employed for the construction of weapons, as uranium and plutonium. New techniques for the inspections of containers should be fast, allow the detection and identification of dangerous materials, and be non-invasive, to reduce costs and delays. We propose to build a large surface photon and neutron detector based on plastic scintillator to identify the presence of fissile or fertile material inside a container. The detector consists of scintillator bars, wrapped in thin foils of reflecting material containing gadolinium for neutron capture and arranged in planes separated by few-millimeter-thick lead sheets. The total instrumented surface is a few squared meters. Neutrons emitted by fissile materials are identified by gadolinium capture, which results in a high multiplicity gamma flash with total energy of 8MeV. Photons emitted by the same source are detected via their Compton interaction in the scintillating material. The discrimination between photons and neutrons is achieved by measuring the number of bars of the detector that measured a signal above threshold. The resulting multiplicity is a clear signature of the particle type. First simulations of the detector response with GEANT4 have shown that a detection efficiency of 20–30% for neutrons emitted by fissile materials and a photon/neutron rejection ratio of more than two orders of magnitude can be achieved. Based on these simulations, the sensitivity of the detector to known amounts of plutonium and uranium was estimated. In this contribution, the conceptual design of the detector will be reviewed, the results of the simulations will be presented and the plan of measurements to be performed on a prototype will be discussed. [Copyright &y& Elsevier]

We discuss two complementary strategies to search for light dark matter (LDM) exploiting the positron beam possibly available in the future at Jefferson Laboratory. LDM is a new compelling hypothesis that identifies dark matter with new sub-GeV "hidden sector" states, neutral under standard model interactions and interacting with our world through a new force. Accelerator-based searches at the intensity frontier are uniquely suited to explore it. Thanks to the high intensity and the high energy of the Continuous Electron Beam Accelerator Facility (CEBAF) beam, and relying on a novel LDM production mechanism via positron annihilation on target atomic electrons, the proposed strategies will allow us to explore new regions in the LDM parameters space, thoroughly probing the LDM hypothesis as well as more general hidden sector scenarios. [ABSTRACT FROM AUTHOR]

The Forward Time-of-Flight system for the large-acceptance CLAS12 spectrometer in Hall B at the Thomas Jefferson National Accelerator Facility is described. The system is positioned at distances in the range from 6.2 m to 7.2 m from the beam–target interaction point and spans laboratory polar angles from 5 ∘ → 4 5 ∘ and nearly the full azimuth. The system consists of 540 individual scintillation counters with double-ended readout that range in length from 17 cm to 426 cm of discrete widths of 6 cm, 15 cm, and 22 cm, and of discrete thicknesses of 5 cm and 6 cm. The effective counter time resolution for passing charged particles varies from 50 ps for the shortest counters at small angles to 200 ps for the longest counters at large angles. The detectors are part of the forward-angle particle identification system for CLAS12 during offline event reconstruction and are a component of the online data acquisition trigger to select final state event topologies with forward-going charged particles. [ABSTRACT FROM AUTHOR]

Background: Conflicting evidence challenges clinical decision‐making when breast reconstruction is considered in the context of radiotherapy. Current literature was evaluated and key statements on topical issues were generated and discussed by an expert panel at the International Oncoplastic Breast Surgery Meeting in Milan 2017. Methods: Studies on radiotherapy and breast reconstruction (1985 to September 2017) were screened using MEDLINE, Embase and CENTRAL. The literature review yielded 30 controversial key questions. A set of key statements was derived and the highest levels of clinical evidence (LoE) for each of these were summarized. Nineteen panellists convened for dedicated discussions at the International Oncoplastic Breast Surgery Meeting to express agreement, disagreement or abstention for the generated key statements. Results: The literature review identified 1522 peer‐reviewed publications. A list of 22 key statements was produced, with the highest LoE recorded for each statement. These ranged from II to IV, with most statements (11 of 22, 50 per cent) supported by LoE III. There was full consensus for nine (41 per cent) of the 22 key statements, and more than 75 per cent agreement was reached for half (11 of 22). Conclusion: Poor evidence exists on which to base patient‐informed consent. Low‐quality studies are conflicting with wide‐ranging treatment options, precluding expert consensus regarding optimal type and timing of breast reconstruction in the context of radiotherapy. There is a need for high‐quality evidence from prospective registries and randomized trials in this field. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the results of an experiment to assess the muon flux produced by the interaction of a 10.6 GeV electron beam with the Hall-A beam dump at Jefferson Lab (JLab). The goal was to benchmark Monte Carlo simulations that are an essential tool for estimating beam-related backgrounds in beam-dump experiments aimed at searching for rare events, such as the Beam Dump eXperiment (BDX) planned at JLab. Beam-produced muons were measured with a CsI(Tl) crystal sandwiched between a set of segmented plastic scintillators placed at two different distances from the dump: 25.7 m and 28.8 m. At each location the muon flux was sampled at different vertical positions with respect to the beam height. Data have been compared with detailed Monte Carlo simulations using FLUKA for the muon production in the dump and propagation to the detector, and GEANT4 to simulate the detector response. The good agreement between data and simulations, within the uncertainties of the soil composition and density, demonstrate the validity of our simulation tools to predict the beam-related muon background in electron beam-dump experiments at ∼ 10 GeV. [ABSTRACT FROM AUTHOR]

A new Radial Time Projection Chamber (RTPC) was developed at the Jefferson Laboratory to track low-energy nuclear recoils to measure exclusive nuclear reactions, such as coherent deeply virtual Compton scattering and coherent meson production off 4 He. In 2009, we carried out these measurements using the CEBAF Large Acceptance Spectrometer (CLAS) supplemented by the RTPC positioned directly around a gaseous 4 He target, allowing a detection threshold as low as 12 MeV for 4 He. This article discusses the design, principle of operation, calibration methods and performances of this RTPC. [ABSTRACT FROM AUTHOR]

Silicon photomultipliers are a novel technology for the detection of photons in near ultraviolet, visible, and near-infrared spectral ranges. Their application is rapidly growing and extending to many fields in physics, replacing traditional PMTs and APDs. In this study a large-size CsI(Tl) crystal coupled to small-area SiPM ( 3 × 3 mm 2 ) was used to detect α -particles and low energy protons. In particular, the detector was irradiated with proton beams accelerated by the Tandem Van-der-Graff of the INFN-Laboratori Nazionali del Sud (LNS), at incident energies between 2.5 MeV and 24 MeV. The detector performance was studied in terms of light yield, linearity and energy resolution. In addition, we investigated the dependence of the detector response on the impact point of the particles. [ABSTRACT FROM AUTHOR]

Several factors can contribute to the difficulty of aligning the sensors of tracking detectors, including a large number of modules, multiple types of detector technologies, and non-linear strip patterns on the sensors. The latter two of these three factors apply to the CLAS12 CVT, which is a hybrid detector consisting of planar silicon sensors with non-parallel strips, and cylindrical micromegas sensors with longitudinal and arc-shaped strips located within a 5 T superconducting solenoid. To align this detector, we used the Kalman Alignment Algorithm, which accounts for correlations between the alignment parameters without requiring the time-consuming inversion of large matrices. This is the first time that this algorithm has been adapted for use with hybrid technologies, non-parallel strips, and curved sensors. We present the results for the first alignment of the CLAS12 CVT using straight tracks from cosmic rays and from a target with the magnetic field turned off. After running this procedure, we achieved alignment at the level of 10 μ m , and the widths of the residual spectra were greatly reduced. These results attest to the flexibility of this algorithm and its applicability to future use in the CLAS12 CVT and other hybrid or curved trackers, such as those proposed for the future Electron-Ion Collider. [ABSTRACT FROM AUTHOR]

This paper describes the veto system of the BDX-MINI detector installed at Jefferson Lab (US). The BDX-MINI experiment is the first electron beam-dump experiment specifically designed to search for Light Dark Matter (LDM) particles in the MeV-GeV mass range. The core of the BDX-MINI detector is a lead-tungstate electromagnetic calorimeter, for a total volume of 4 dm 3. The calorimeter is surrounded by a multi-layer veto aimed at rejecting cosmic background: the innermost layer of the veto is made by a passive tungsten shielding for low energy radiation, while plastic scintillators make the middle and outer layers for charged cosmic particles rejection. Being located about 20 m downstream, the dirt between the beam dump and the detector provides sufficient shielding from the beam-related background. In 2019–2020, BDX-MINI was exposed for about six months to weakly interacting particles (neutrinos and, if existing, DM) produced by a 2.176 GeV electron beam incident on the beam dump of experimental Hall-A at Jefferson Lab. [ABSTRACT FROM AUTHOR]

The well-established technology of electromagnetic calorimetry using Lead Tungstate crystals has recently seen an upheaval, with the closure of one of the most experienced large-scale suppliers of such crystals, the Bogoroditsk Technical Chemical Plant (BTCP), which was instrumental in the development of mass production procedures for PWO-II, the current benchmark for this scintillator. Obtaining alternative supplies of Lead Tungstate crystals matching the demanding specifications of contemporary calorimeter devices now presents a significant challenge to detector research and development programmes. In this paper we describe a programme of assessment carried out for the selection, based upon the performance under irradiation, of Lead Tungstate crystals for use in the Forward Tagger device, part of the CLAS12 detector in Hall B at Jefferson Lab. The crystals tested were acquired from SICCAS, the Shanghai Institute of Ceramics, Chinese Academy of Sciences. The tests performed are intended to maximise the performance of the detector within the practicalities of the crystal manufacturing process. Results of light transmission, before and after gamma ray irradiation, are presented and used to calculate dk , the induced radiation absorption coefficient, at 420 nm, the peak of the Lead Tungstate emission spectrum. Results for the SICCAS crystals are compared with identical measurements carried out on Bogoroditsk samples, which were acquired for the Forward Tagger development program before the closure of the facility. Also presented are a series of tests performed to determine the feasibility of recovering radiation damage to the crystals using illumination from an LED, with such illumination available in the Forward Tagger from a light monitoring system integral to the detector. [ABSTRACT FROM AUTHOR]

The series of workshops on New Partial-Wave Analysis Tools for Next-Generation Hadron Spectroscopy Experiments was initiated with the ATHOS 2012 meeting, which took place in Camogli, Italy, June 20-22, 2012. It was followed by ATHOS 2013 in Kloster Seeon near Munich, Germany, May 21-24, 2013. The third, ATHOS3, meeting is planned for April 13-17, 2015 at The George Washington University Virginia Science and Technology Campus, USA. The workshops focus on the development of amplitude analysis tools for meson and baryon spectroscopy, and complement other programs in hadron spectroscopy organized in the recent past including the INT-JLab Workshop on Hadron Spectroscopy in Seattle in 2009, the International Workshop on Amplitude Analysis in Hadron Spectroscopy at the ECT*-Trento in 2011, the School on Amplitude Analysis in Modern Physics in Bad Honnef in 2011, the Jefferson Lab Advanced Study Institute Summer School in 2012, and the School on Concepts of Modern Amplitude Analysis Techniques in Flecken-Zechlin near Berlin in September 2013. The aim of this document is to summarize the discussions that took place at the ATHOS 2012 and ATHOS 2013 meetings. We do not attempt a comprehensive review of the field of amplitude analysis, but offer a collection of thoughts that we hope may lay the ground for such a document. The material presented in the article was edited by the following Editorial Board: Marco Battaglieri, Bill J. Briscoe, Su-Urk Chung, Michael Döring, Józef Dudek, Geoffrey Fox, Christoph Hanhart, Martin Hoferichter, David G. Ireland, Bernhard Ketzer, Bastian Kubis, Vincent Mathieu, Ryan Mitchell, José R. Peláez, Elena Santopinto, Adam Szczepaniak. [ABSTRACT FROM AUTHOR]

Abstract: A single-crystal CVD (Chemical Vapor Deposition) diamond detector was used to measure γ rays in order to assess its performance in terms of energy resolution and linearity. For this purpose, 57Co, 133Ba, 22Na, 207Bi and 137Cs γ sources were used. Electrons scattered by the backward Compton process were detected in the diamond, in coincidence with (backscattered) γs measured in a NaI detector, placed at 180° from the CVD diamond detector with respect to the source. The resulting calibration shows a linear dependence of the charge deposited in the diamond and a resolution of about 24keV FWHM for the energy of the incident γs between 40keV (57Co) and 477keV (137Cs), comparable with the resolution of our electronic chain. [Copyright &y& Elsevier]

Abstract: In this article we describe the properties of a new 10-in. hemispherical photomultiplier manufactured by Hamamatsu. The prototype has a segmented photocathode and four independent amplification stages. The photomultiplier is one of the main components of a newly designed direction-sensitive optical module to be employed in large-scale underwater neutrino telescopes. The R&D activity has been co-funded by the INFN and the KM3NeT Consortium. The prototype performance fully meets with the design specifications. [Copyright &y& Elsevier]

We present new data on the Bjorken sum Γ ‾ 1 p − n (Q 2) at 4-momentum transfer 0.021 ≤ Q 2 ≤ 0.496 GeV2. The data were obtained in two experiments performed at Jefferson Lab: EG4 on polarized protons and deuterons, and E97110 on polarized 3He from which neutron data were extracted. The data cover the domain where chiral effective field theory (χ EFT), the leading effective theory of the Strong Force at large distances, is expected to be applicable. We find that our data and the predictions from χ EFT are only in marginal agreement. This is somewhat surprising as the contribution from the Δ (1232) resonance is suppressed in this observable, which should make it more reliably predicted by χ EFT than quantities in which the Δ contribution is important. The data are also compared to a number of phenomenological models with various degrees of agreement. [ABSTRACT FROM AUTHOR]

Abstract: The study of the response of the two modules of the large-angle electromagnetic shower calorimeter of the CLAS detector to charged and neutral particles is reported. The results agree very well with the Monte Carlo simulation. The procedures adopted for the energy and timing calibration are also discussed, proving that the module geometry allows for simple self-calibrating energy and timing algorithms. [Copyright &y& Elsevier]

The difference of the cross sections for double charged-pion production in the scattering of opposite-helicity electrons on an unpolarized proton is evaluated within the phenomenological model developed previously. The electromagnetic nucleon-resonance form factors and the parameters of nonresonance processes were taken from a fit to the latest data of the CLAS Collaboration on double charged-pion electroproduction. The effect of the longitudinal excitations of the P11(1440) and D13(1520) states on the difference of the helicity components of the cross section is studied. The sensitivity of this observable to the nucleon-resonance contribution opens the possibility of employing it both in extracting the Coulomb form factors and in seeking new baryon states. Signals from one of these states were possibly observed in the latest data of the CLAS Collaboration.© 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

A model for describing the double charged-pion production by real and virtual photons in the energy region of nucleon-resonance excitation is further developed for calculating the angular distributions of reaction products off the scattering plane and the beam asymmetry. It is shown that investigation of these observables has a rich potential for extracting the first data on the Coulomb excitation of many nucleon resonances and for separating the contributions of various helicity amplitudes to the excitation of nucleon resonances by transverse photons.© 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The helicity components σ[sub ½] and σ[sub 3/2] of the cross section for double charged-pion production by real photons on a nucleon are calculated within a phenomenological approach developed previously. A high sensitivity of the σ[sub ½]-σ[sub 3/2] asymmetry to the contribution of nucleon resonances having strongly different electromagnetic helicity amplitudes A[sub ½] and A[sub 3/2] is demonstrated. This feature is of importance for seeking "missing" baryon states. [ABSTRACT FROM AUTHOR]

We describe the design, construction, and performance of a polarized solid target for use in electron scattering experiments with the CEBAF Large Acceptance Spectrometer. Protons and deuterons are continuously polarized by microwave-induced spin–flip transitions at 1 K and 5 T. The target operated successfully during two cycles in 1998 and 2000, providing proton and deuteron polarizations as high as 96% and 46%, respectively. The unique features of the target which permit its use inside a 4π spectrometer are stressed. Comparison is made between the target polarization measured by the traditional method of NMR and by electron elastic scattering. [Copyright &y& Elsevier]

The CLAS12 Data Acquisition System was designed and built as part of the CLAS12 detector project in Hall B at Jefferson Laboratory. This article contains a full description of the system, including requirements, design, hardware, and software descriptions, as well as the achieved performance. The associated computing, network, and slow controls systems are also described. [ABSTRACT FROM AUTHOR]

The Central Time-of-Flight system for the large-acceptance CLAS12 spectrometer in Hall B at the Thomas Jefferson National Accelerator Facility is described. The system consists of a hermetic barrel of 48 scintillation counters at a radius of 25 cm from the beamline. The wedge-shaped counters are 3.4 cm wide, 3.0 cm thick, and 90 cm long, and span a range of polar angles relative to the center of the nominal target location from roughly 35 ∘ to 125 ∘. The counters reside in the 5-T field of the CLAS12 superconducting solenoid. The bars are read out via bent light guides 1 m long on the upstream end of the counters and 1.6 m long on the downstream end. The phototubes are shielded by a multi-layer dynamical magnetic shield system to reduce the local fringe fields in the range from 400 G to 1000 G down to the level of 0.2 G at the location of the photocathodes. The average effective time resolution of the counters is 80 ps. [ABSTRACT FROM AUTHOR]

We describe offline event reconstruction for the CEBAF Large Acceptance Spectrometer at 12 GeV (CLAS12), including an overview of the offline reconstruction framework and software tools, a description of the algorithms developed for the individual detector subsystems, and the overall approach for charged and neutral particle identification. We also present the scheme for data processing and the code management procedures. [ABSTRACT FROM AUTHOR]

The Geant4 Monte-Carlo (GEMC) package is used to simulate the passage of particles through the various CLAS12 detectors. The geometry is implemented through a database of Geant4 volumes created either through the GEMC native API, by the CLAS12 geometry service, or imported from the CAD engineering model. The truth information is digitized with a plugin mechanism by routines specific to each detector and includes the use of the CLAS12 calibration database constants to produce both ADC and TDC response functions. Theoretical models that produce the generated events interface with GEMC through the LUND data format. The merging of simulated data with real random trigger data provides a mechanism to include both beam and electronic background into the simulation of generated events to accurately model beam data from the CLAS12 detector. The performance of simulation is demonstrated by comparison with the experimental data. [ABSTRACT FROM AUTHOR]

This paper describes the Hall B beamline and its performance during the first year of data-taking operation using the CLAS12 detector. We review the beamline instrumentation used to measure and monitor the beam. This instrumentation led to excellent beam quality for energies ranging from 2.2 to 10.6 GeV at the design luminosity of 1 0 35 cm−2s−1. The instrumentation includes a Møller polarimeter, which can typically measure the beam polarization to an absolute precision of ∼ 2.5%. [ABSTRACT FROM AUTHOR]

Longitudinal phase space analyses as introduced by van Hove provided a simplified method of separating different reaction production mechanisms. Cuts in the longitudinal phase space can help to select specific reaction kinematics but also induce nonflat acceptance effects in angular distributions. We show that in photoproduction reactions dominated by t-channel exchanges, selection of meson or baryon production over a large mass range can be optimized through calculating mass-dependent cut limits compared to cuts on a van Hove plot sector alone. A cut is presented that improves this selection of one type of hadron production by rejecting another. In addition we demonstrate that using cuts in longitudinal phase space preserves sufficient information to reliably extract observables from the angular distribution of the final state particles. [ABSTRACT FROM AUTHOR]

A novel mechanism to produce and detect light dark matter in experiments making use of GeV electrons (and positrons) impinging on a thick target (beam dump) is proposed. The positron-rich environment produced by the electromagnetic shower allows us to produce an A′ via nonresonant (e++e-→γ+A′) and resonant (e++e-→A′) annihilation on atomic electrons. The latter mechanism, for some selected kinematics, results in a larger sensitivity with respect to limits derived by the commonly used A′-strahlung. This idea, applied to beam-dump experiments and active beam-dump experiments, pushes down the current limits by an order of magnitude. [ABSTRACT FROM AUTHOR]