A computational model of spasticity based on a decoupling of the alpha and gamma efferents

It is generally accepted that spasticity results from changes in the excitability of the stretch reflex. This change lowers the threshold of the motoneurons of the spinal cord where the integration of a signal from velocity/position sensors is processed and then fed back to the contracting muscle (alphaextrafusal and gamma-intrafusal fibers). The stretch reflex depends on the initial length of the muscle, the stretch velocity and voluntary activity. The exact sequence of the triggering events remains unknown, is poorly understood and as a result is controversial. The clinical classification scales are mainly subjective and by definition, inaccurate. This computational model of spasticity is based on the concept of the existence of a normal neuromuscular control coupling function, which ordinarily encloses the extrafusal and intrafusal fibers, and explains the spasticity as a result of the uncoupling of this normal mechanism. The model involves mechanical parameters and basic neuromuscular control theory

Novel model of cerebrospinal fluid dynamics based on hemodynamically driven cyclic brain compliance variation

This study provides a novel explanation for the CerebrQ-Spinal Fluid (CSF) flow pattern observed in phase contrast cine-MRJ studies. CSF dynamics has been traditionally explained as a bulk flow from the site of production to the site of absorption. Studies done with phase contrast cine-MRI show a more complex CSF movement, that is not explainable by the bulk flow paradigm. This study describes a mechanism explaining how the energy delivered by the heart in each cycle is responsible not only for the blood flow, but also for the CSF circulation. This mechanism is based on a cyclic variation of brain compliance, dependent on the blood volume inside the brain vessels. As the cardiac cycle changes the blood volume inside the vessels, it also conditions a compliance cycle of the brain tissue. For better comprehension of the mechanism, a conceptual model, mathematical model and computer model are described. To capture the essence of CSF dynamics a three compartmental model is created representing: the ventricular system, the intracranial subarachnoideal space, and the spinal subarachnoideal space. The implemented driving function represents the blood volume variation with time produced by the cardiac cycle. In turn it detennines cyclic changes in brain parenchyma compliance. Brain parenchyma compliance changes as a function of the blood volume inside the brain vessels; therefore, during systole the compliance diminishes, during diastole compliance increases. As brain tissue compliance changes the CSF volume inside each compartment is redistributed. Cyclic compliance variation of brain tissue creates a pulsatile CSF flow. The CSF dynamics model is also used for the analysis of altered CSF dynamics; Normal Pressure Hydrocephalus and Idiopathic Intracranial Hypertension are explained as a consequence of altered compliance of the brain tissue

Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV

The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8  TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum

Selection of the silicon sensor thickness for the Phase-2 upgrade of the CMS Outer Tracker

During the operation of the CMS experiment at the High-Luminosity LHC the silicon sensors of the Phase-2 Outer Tracker will be exposed to radiation levels that could potentially deteriorate their performance. Previous studies had determined that planar float zone silicon with n-doped strips on a p-doped substrate was preferred over p-doped strips on an n-doped substrate. The last step in evaluating the optimal design for the mass production of about 200 m$^{2}$ of silicon sensors was to compare sensors of baseline thickness (about 300 μm) to thinned sensors (about 240 μm), which promised several benefits at high radiation levels because of the higher electric fields at the same bias voltage. This study provides a direct comparison of these two thicknesses in terms of sensor characteristics as well as charge collection and hit efficiency for fluences up to 1.5 × 10$^{15}$ n$_{eq}$/cm$^{2}$. The measurement results demonstrate that sensors with about 300 μm thickness will ensure excellent tracking performance even at the highest considered fluence levels expected for the Phase-2 Outer Tracker

Beam test performance of a prototype module with Short Strip ASICs for the CMS HL-LHC tracker upgrade

The Short Strip ASIC (SSA) is one of the four front-end chips designed for the upgrade of the CMS Outer Tracker for the High Luminosity LHC. Together with the Macro-Pixel ASIC (MPA) it will instrument modules containing a strip and a macro-pixel sensor stacked on top of each other. The SSA provides both full readout of the strip hit information when triggered, and, together with the MPA, correlated clusters called stubs from the two sensors for use by the CMS Level-1 (L1) trigger system. Results from the first prototype module consisting of a sensor and two SSA chips are presented. The prototype module has been characterized at the Fermilab Test Beam Facility using a 120 GeV proton beam

Comparative evaluation of analogue front-end designs for the CMS Inner Tracker at the High Luminosity LHC

The CMS Inner Tracker, made of silicon pixel modules, will be entirely replaced prior to the start of the High Luminosity LHC period. One of the crucial components of the new Inner Tracker system is the readout chip, being developed by the RD53 Collaboration, and in particular its analogue front-end, which receives the signal from the sensor and digitizes it. Three different analogue front-ends (Synchronous, Linear, and Differential) were designed and implemented in the RD53A demonstrator chip. A dedicated evaluation program was carried out to select the most suitable design to build a radiation tolerant pixel detector able to sustain high particle rates with high efficiency and a small fraction of spurious pixel hits. The test results showed that all three analogue front-ends presented strong points, but also limitations. The Differential front-end demonstrated very low noise, but the threshold tuning became problematic after irradiation. Moreover, a saturation in the preamplifier feedback loop affected the return of the signal to baseline and thus increased the dead time. The Synchronous front-end showed very good timing performance, but also higher noise. For the Linear front-end all of the parameters were within specification, although this design had the largest time walk. This limitation was addressed and mitigated in an improved design. The analysis of the advantages and disadvantages of the three front-ends in the context of the CMS Inner Tracker operation requirements led to the selection of the improved design Linear front-end for integration in the final CMS readout chip

The CMS Phase-1 pixel detector upgrade

The CMS detector at the CERN LHC features a silicon pixel detector as its innermost subdetector. The original CMS pixel detector has been replaced with an upgraded pixel system (CMS Phase-1 pixel detector) in the extended year-end technical stop of the LHC in 2016/2017. The upgraded CMS pixel detector is designed to cope with the higher instantaneous luminosities that have been achieved by the LHC after the upgrades to the accelerator during the first long shutdown in 2013–2014. Compared to the original pixel detector, the upgraded detector has a better tracking performance and lower mass with four barrel layers and three endcap disks on each side to provide hit coverage up to an absolute value of pseudorapidity of 2.5. This paper describes the design and construction of the CMS Phase-1 pixel detector as well as its performance from commissioning to early operation in collision data-taking.Peer reviewe

Evidence for X(3872) in Pb-Pb Collisions and Studies of its Prompt Production at sNN\sqrt{^{s}NN} =5.02 TeV

The first evidence for X(3872) production in relativistic heavy ion collisions is reported. The X(3872) production is studied in lead-lead (Pb-Pb) collisions at a center-of-mass energy of $\sqrt{^{s}NN}$=5.02 TeV per nucleon pair, using the decay chain X(3872)→J/ψπ$^{+}$ π$^{–}$→μ$^{+}$μ$^{–}$π$^{+}$ π$^{–}$. The data were recorded with the CMS detector in 2018 and correspond to an integrated luminosity of 1.7 nb$^{-1}$. The measurement is performed in the rapidity and transverse momentum ranges |y|<1.6 and 15<pT<50 GeV/c. The significance of the inclusive X(3872) signal is 4.2 standard deviations. The prompt X(3872) to ψ2S yield ratio is found to be ρ$^{Pb-Pb}$=1.08±0.49(stat)±0.52(syst), to be compared with typical values of 0.1 for pp collisions. This result provides a unique experimental input to theoretical models of the X(3872) production mechanism, and of the nature of this exotic state

Measurement of the Y(1S) pair production cross section and search for resonances decaying to Y(1S)μ⁺μ⁻ in proton-proton collisions at √s = 13 TeV

The fiducial cross section for Y(1S) pair production in proton-proton collisions at a center-of-mass energy of 13 TeV in the region where both Y(1S) mesons have an absolute rapidity below 2.0 is measured to be 79±11(stat)±6(syst)±3(B) pb assuming the mesons are produced unpolarized. The last uncertainty corresponds to the uncertainty in the Y(1S) meson dimuon branching fraction. The measurement is performed in the final state with four muons using proton-proton collision data collected in 2016 by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9fb⁻¹. This process serves as a standard model reference in a search for narrow resonances decaying to Y(1S)μ⁺μ⁻ in the same final state. Such a resonance could indicate the existence of a tetraquark that is a bound state of two b quarks and two b antiquarks. The tetraquark search is performed for masses in the vicinity of four times the bottom quark mass, between 17.5 and 19.5 GeV, while a generic search for other resonances is performed for masses between 16.5 and 27 GeV. No significant excess of events compatible with a narrow resonance is observed in the data. Limits on the production cross section times branching fraction to four muons via an intermediate Y(1S) resonance are set as a function of the resonance mass

The production of isolated photons in PbPb and pp collisions at sNN \sqrt{s_{\mathrm{NN}}} = 5.02 TeV

The transverse energy (E$_{T}^{γ}$) spectra of photons isolated from other particles are measured using proton-proton (pp) and lead-lead (PbPb) collisions at the LHC at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV TeV with integrated luminosities of 27.4 pb$^{-1}$ and 404 μb$^{-1}$ for pp and PbPb data, respectively. The results are presented for photons with 25 <E$_{T}^{γ}$< 200 GeV in the pseudorapidity range |η| < 1.44, and for different centrality intervals for PbPb collisions. Photon production in PbPb collisions is consistent with that in pp collisions scaled by the number of binary nucleon-nucleon collisions, demonstrating that photons do not interact with the quark-gluon plasma. Therefore, isolated photons can provide information about the initial energy of the associated parton in photon+jet measurements. The results are compared with predictions from the next-to-leading-order jetphox generator for different parton distribution functions (PDFs) and nuclear PDFs (nPDFs). The comparisons can help to constrain the nPDFs global fits