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Essential tremor (ET) is one of the most common movement disorders with heterogeneous pathogenesis involving both genetic and environmental factors, which often results in variable therapeutic outcomes. Despite the diverse etiology, ET is defined by a core symptom of action tremor, an involuntary rhythmic movement that can be mathematically characterized by two parameters: tremor frequency and tremor amplitude. Recent advances in neural dynamics and clinical electrophysiology have provided valuable insights to explain how tremor frequency and amplitude are generated within the central nervous system. This review summarizes both animal and clinical evidence, encompassing the kinematic features of tremors, circuitry dynamics, and the neuronal coding mechanisms for the two parameters. Neural population coding within the olivocerebellum is implicated in determining tremor frequency, while the cerebellar circuitry synchrony and cerebellar-thalamo-cortical interactions play key roles in regulating tremor amplitude. Novel therapeutic strategies aimed at tuning tremor frequency and amplitude are also discussed. These neural dynamic approaches target the conserved mechanisms across ET patients with varying etiologies, offering the potential to develop universally effective therapies for ET. [ABSTRACT FROM AUTHOR]

The three-dimensional propagation of stationary planetary waves in the linearized baroclinic quasi-geostrophic model is investigated by applying wave propagation theory. The variations in wave energy and amplitude along energy propagation paths or called rays are further derived by applying a method that can resolve changes in the magnitude of the group velocity. The results suggest that there exists a meridional wave guide in the middle troposphere, where waves mainly propagate meridionally and are reflected by two turning altitudes that are located in the lower and upper troposphere, respectively. There also exists a vertical wave guide in high latitudes to permit vertical propagation for rays. This wave guide is a key region for enabling interactions between the troposphere and stratosphere, particularly favoring waves with larger scales. Besides, the vertical propagation of waves is modulated by seasonal variations in the zonal basic flow and temperature. Both wave energy and amplitude can approach to the local maxima at turning altitudes and latitudes if the basic state undergoes minor changes, indicating that waves may have a substantial development when they move toward these turning locations. By defining an instability criterion and specifying a simple zonal basic flow such as a jet prototype, the instability of baroclinic waves can be further explored. [ABSTRACT FROM AUTHOR]

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Magnesium (Mg) alloys have high specific strength and are widely employed in aerospace and automotive industries. Gas tungsten arc welding (GTAW) is an important method for welding and repairing magnesium alloys. However, magnesium alloys have high hot cracking sensitivity during welding, especially in the Mg-aluminum (Al) alloys with high Al contents. In this study, the application and mechanism of ultrasonic-assisted gas tungsten arc welding (U-GTAW) in reducing the susceptibility of hot cracks in magnesium alloys during welding were discussed. The results showed that the crack rate, grain size, and β-phase size decreased as the ultrasonic amplitude increased. The crack initiation process, crack tip morphology, and crack fracture morphology were observed. Ultrasonic cavitation, acoustic flow, and ultrasonic capillary effect would result in decrease grain size, fine dispersion of the β-phase and improve the healing ability of liquid phase. With the increase of ultrasonic amplitude, the hot crack sensitivity of U-GTAW decreased. [ABSTRACT FROM AUTHOR]

Seven-day actigraphy was performed within 1 month in 122 community-dwelling adults (mean age 24.40 y, 31 (25.4%) men) in the same city of Tyumen, Russia. Groups with different COVID-19 status (present, COVID-19(+), n = 79 vs absent, COVID-19(−), n = 43) did not differ in mean age, gender distribution, or body mass index. Vaccination status was equally represented in the COVID groups. We found that COVID-19 status, a history of SARS-CoV-2 infection, was differentially associated with daylight susceptibility. Daylight exposure was estimated using parametric and non-parametric indices: 24-h Amplitude, MESOR or M10 of white and blue light exposure (BLE) and compared between the groups. Distinctively in COVID-19(+) individuals, a smaller normalized 24-h amplitude of BLE (NAbl) was associated with lower circadian robustness, assessed by a smaller relative non-parametric amplitude (RA), a lower circadian function index (CFI), later bedtime, later onset of least active 5 h (L5), shorter total sleep duration, later phase and smaller circadian amplitude of physical motor activity. Such associations were absent in the overall COVID-19(−) population or in the vaccinated COVID(−) group. Considering COVID-status and light hygiene, defined as NAbl ≥ 1 versus NAbl < 1, only those with COVID(+) and NAbl < 1 (poorer light hygiene) had a statistically significantly delayed phase of activity and sleep, reduced circadian amplitude of physical activity, and lower circadian robustness. Accounting for gender and BMI, participants diagnosed with COVID-19 at an earlier date were older and had poorer circadian light hygiene. Altogether, our data suggest that those with COVID-19 were more vulnerable to circadian disruption due to poor circadian light hygiene, manifested as phase delay, small amplitude, a less robust circadian pattern of activity, and as delayed sleep. Our data suggest that the need for optimal circadian light hygiene is greater in individuals with a history of SARS-CoV-2 infection. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the effect of induced excitation of the bottom-up pathways at the lateral elbow muscles on local muscle fatigue in the neck region in healthy participants. Eligible participants (n:55) were randomly allocated to an intervention group (n:28) or a control group (n:27). The fatigue of bilateral neck flexor(sternocleidomastoid) and extensor (upper trapezius) muscles was evaluated using surface electromyography, at baseline and immediately post-intervention during a neck flexor and extensor endurance test respectively. Excitation of the bottom-up pathways was performed at multiple lateral elbow muscles in the intervention group by using a temporal summation protocol of mechanical pain, and the pressure pain threshold was determined once in each of the multiple lateral elbow muscles in the control group. Linear mixed model analyses were performed for each outcome measure to evaluate changes over time and within- and between-group differences. No significant “group X time” interaction effects were detected for any of the outcome measures. Significant main effects for time was found for “amplitude over time” of the left upper trapezius (p:0.003) and right sternocleidomastoid muscle (p: 0.013), and for “amplitude changes” of the left upper trapezius muscle (p:0.021). Significant within-group changes were identified in some outcomes in the control group: increased “amplitude over time” of the right sternocleidomastoid muscle (p:0.024) and decreased “amplitude changes” of the left upper trapezius muscle (p:0.024), decreased “normalized median frequency slope over time” of the left UT (p: 0.013). There were no significant within-group changes in the intervention group. No significant between-group differences for any of the outcome measures were found. This study shows no effect of the induction of excitation of the bottom-up pathways at the lateral elbow muscles on the neck muscles’ fatigue characteristics compared to a control intervention. Clinical Trial Number: NCT05146960. Date of Registration: December 7, 2021. [ABSTRACT FROM AUTHOR]

This paper presents two-dimensional numerical simulations of the self-excited forces on two bridge decks: a streamlined one (Great Belt Bridge) and a bluff one (Sunshine Skyway Bridge). It employs forced vibration simulations using the Open-source code OpenFOAM for flutter derivative identifications. A wide sensitivity study is conducted on the effects of turbulence model, Reynolds number, vibration amplitude, and wind attack angle on flutter derivative identifications. The key findings are as follows. (i) k-ε model shows its superiority in simulating self-excited forces on a bluff bridge deck, while SST k-ω exhibits advantages in the case of a streamlined bridge deck. (ii) Compared with a streamlined bridge deck, flutter derivatives of a bluff bridge deck are more sensitive to the Reynolds number due to the generation of more vortices resulting from flow separation. Both the generation and convection of the vortices are largely affected by the Reynolds number. (iii) Flutter derivatives of the bridge decks can be considered as constants if the vertical amplitude ratio and torsional amplitude are lower than 0.025 and 2°, respectively. Increasing vibration amplitude may result in remarkable variations of some flutter derivatives. (iv) The angle of attack changes the flutter derivatives by affecting the wind pressure distribution on the bridge surface. Its impact on a bluff bridge deck is larger than on a streamlined bridge deck. Besides presenting a detailed study of identifying flutter derivatives using OpenFOAM, this research provides valuable references for setting reasonable values of the investigated factors for identifying flutter derivatives of bluff and streamlined bridge decks.

Abstract Humans sometimes synchronize their steps to mechanical oscillations in the environment (e.g., when walking on a swaying bridge or with a wearable robot). Previous studies have discovered discrete frequencies and/or amplitudes where individuals spontaneously synchronize to external oscillations, but these parameters are often chosen arbitrarily or for convenience of a successful experiment and are sparsely sampled due to time constraints on subject availability. As a result, the parameter space under which human gait synchronization occurs is still relatively underexplored. Here we systematically measure synchronization over a broad range of parameters in machine oscillations, applied vertically near the body center of mass during walking. Two complementary experiments were utilized to characterize the amplitudes and frequencies where subjects’ gait matched the oscillation frequency within ± 0.02 Hz for at least 80% of 20 consecutive steps (i.e., synchronization). Individuals were found to synchronize at lower amplitudes and in less time when the oscillation frequency was nearer their baseline step frequency, as well as over a broader range of frequencies during larger oscillation amplitudes. Subjects also had a greater tendency to synchronize with oscillation frequencies below (rather than above) their baseline step frequencies. The results of this study provide a comprehensive mapping of parameters where synchronization occurs and could inform the design of exoskeletons, rehabilitation devices and other gait-assistive technologies.

Introduction/aims: In healthy subjects, we observed high amplitude motor unit potential (MUP) waveforms that resembled the cannula potential (CP) with a positive sharp wave (PSW)-like waveform. We analyzed the source of this signal, its prevalence, and its effects on the analysis of electromyographic waveforms., Methods: Three channel recordings were performed to explore the contribution of the needle core and cannula to the MUP. In 7 control subjects with no neuromuscular disease, the EMG interference pattern was quantified for the amplitude asymmetry (AASM) of its positive and negative going peaks., Results: The large amplitude MUP resembling a CP with a PSW-type waveform is recorded by the needle core, not the cannula. With a slight change in needle position, its amplitude decreased and the waveform had a normal appearance. Thus, it is an artifact. Such potentials (AASM > 150%) are commonly encountered (frequency 7%) and occur in all muscles and subjects in this study., Discussion: The artifact is an enigma and appears related to the interaction between the needle and muscle fiber(s) similar to that in PSW signals. Failure to recognize these waveforms may result in a false impression of abnormality. AASM calculations can help confirm this artifact in automated analysis algorithms to preclude false positive neurogenic patterns., (© 2024 Wiley Periodicals LLC.)