Deceleration Forces Research Articles

Ballistic impact response of reinforced concrete panels subjected to diverse multiple projectile impact scenarios: A numerical study

Concrete has wide applications in civil and military infrastructures. Thorough ballistic damage evaluation of these structures is crucial to safeguard these structures against potential threats. Past studies on reinforced concrete (RC) panels primarily focused on single-impact scenarios. However, real-world situations often involve multiple impacts that need to be examined. Hence, this paper critically examines multiple impact scenarios on RC panels to provide a realistic understanding of their ballistic resilience. A three-dimensional finite element model was developed and validated with the experimental data from the literature to simulate the impact of a 2 kg hemispherical-nosed projectile on an RC panel. Extended analyses further investigated the RC panel subjected to multiple impact scenarios. Four distinct scenarios were studied: (1) single impacts at four separate locations, (2) simultaneous impacts at these four locations, (3) sequential impacts of four projectiles, and (4) single projectile impact with energy equivalent to the combined impact of the four projectiles. The study assessed local damage failures, including penetration depth, crater formation, energy absorption, deceleration and reaction forces on projectiles. Results revealed reduced ballistic performance of RC panels under multiple impacts compared to single impacts. Specifically, simultaneous impacts (case 2) and the equivalent single impact (case 4) caused more damage in terms of spalling and scabbing than single impacts (case 1) and sequential impacts (case 3). Additionally, cases 2 and 4 exhibited similar performance in terms of projectile penetration. This study is useful in understanding RC panels’ ballistic performance under multiple impacts.

Bouldering & chronic traumatic encephalopathy – That is repeated mild traumatic brain injury from climbing

Mild traumatic brain injury (mTBI) is one of the most common neurological conditions resulting from linear accelerations in the range of 60 gravity. Chronic traumatic encephalopathy (CTE) is a progressive neurodegenerative syndrome. Its etiopathology is attributed to repeated blows to the head and the transmission of acceleration and deceleration forces to the brain. There are several types of climbing, the most popular are lead climbing, speed climbing and bouldering. Athletes involved in the latter sub-discipline (bouldering) appear to be most at risk of mTBI. Bouldering takes place on artificial walls or natural rock and involves climbing without a rope on routes up to several metres in height. We hypothesised that climbers in the bouldering sub-discipline are at risk of frequent mTBI and, as a consequence, may suffer from chronic traumatic encephalopathy. In the paper we presented physical formula to support our thesis, a verification of this formula and a survey of boulder climbers. The physical model was verified in a practical test. Differences in the range of ≈ 2g were demonstrated (MAE = 1.86, RMSE = 2.51). There is evidence in the form of a physiological model that boulderers are able to achieve accelerations that cause mTBI. The study population had a 12 % incidence of repeated falls and reported symptoms associated with mTBI during bouldering training sessions. Given the diagnosis of CTE, which can only be made after death, future research should focus on diagnosing and treating symptoms of mTBI and CTE (including depression, progressive memory loss, suicidal behaviour, cognitive impairment) in boulder climbers.

Kinetic and Kinematic Characteristics Underpinning Change of Direction Performance in Basketball: A Comparative Study Between Sexes and Tests.

Baena-Raya, A, Díez-Fernández, DM, Martínez-Rubio, C, Conceição, F, and López-Sagarra, A. Kinetic and kinematic characteristics underpinning change of direction performance in basketball: A comparative study between sexes and tests. J Strength Cond Res 38(4): e182-e188, 2024-This study (a) evaluated the sex-specific kinetic and kinematic outcomes underpinning change of direction (COD) performance, (b) compared these outcomes across 3 different COD tests, and (c) examined the sex-specific and test-specific outcome most strongly related to COD performance in basketball players. Thirty young basketball players (17 males and 13 females) competing at the national level were assessed for the modified 505 test, modified T test, and V-cut test. The Local Positioning System technology (WIMU PRO, Realtrack Systems S.L., Almería, Spain) was used to measure the maximum values of acceleration (ACC max ), deceleration (DEC max ), velocity (VEL max ), and centripetal force (CentF max ) in each COD test. Male players displayed greater ACC max , VEL max , DEC max , and CentF max outputs for each section of the 505 test, T test, and V-cut test (all p < 0.05), resulting in a faster COD performance than females across tests (all ES > -1.42; 95% CI = -3.45 to -0.57). The 505 test demanded significantly greater kinematic outputs than T test and V-cut test for both sexes ( p < 0.01). The ACC max explained ∼26-58% of the variability in COD time for males across tests ( p < 0.05) and 40% in females' modified 505-test time ( p < 0.05). Likewise, in females, DEC max explained 38% of the modified T -test time variability, whereas VEL max explained 53% in the V-cut test time (both p < 0.05). These findings suggest that (a) COD data should not be used interchangeably across sexes, (b) test specificities should be considered for designing COD training, and (c) the kinematic outcomes explaining COD performance might vary across sexes.

Localized shear strength mobilization at geosynthetic interfaces caused by spreading soil downslope

Localized interface shear strength failures have occurred below the tracks of a bulldozer during placement and spreading of cover soils on slopes lined with geosynthetics. The mechanisms of these types of failures are rarely considered and evaluated in design reports and calculations. A paper on this subject was recently published by Thiel and Giroud [1], but the analyses presented in that paper were limited to upslope bulldozer pushing. The present paper extends those analyses to consider downslope bulldozer pushing and deceleration forces. The paper presents straightforward equations of equilibrium that the user can easily input into a spreadsheet to model various geometries, bulldozer sizes, and shear strengths, and to determine the acceptable size of the soil pile being pushed for those conditions. The equations provided should be useful for design engineers to avoid localized slippage on slopes where bulldozers are spreading soil materials over geosynthetics, or for forensic experts who evaluate why slippage may have occurred.

The Use of Transition Curves in Airport Runway Rapid Exit Taxiways (RETs)

This paper describes a study result focused on the transition curves used in airport rapid exit taxiways (RETs). Such geometric elements are not currently made explicit by standards, and major international government agencies, such as the International Civil Aviation Organization and the Federal Aviation Administration, are limited to providing some layouts consisting of only constant curvature elements, although the aircrafts speed in RETs is variable. In addition to the clothoid that has unitary shape parameter “n” and the multiparameter clothoids (generalized Cornu spirals), the study analyzes the Bloss curve employment. Regarding the multiparameter clothoids, four schemes with shape parameter equal to 1.25, 1.50, 1.75, and 2.00 were considered, respectively. The proposed curves’ effectiveness was evaluated by analyzing the main geometric and kinematic variables trend, that is, curvature, transversal acceleration, lateral jerk, speed, travel time, longitudinal deceleration, and centrifugal force. To ensure the analysis effectiveness, the study layouts were designed from those used for runways codes 1‐2 and 3‐4 maintaining the main geometric elements dimensions unchanged (length of straight lines, radii of circular curves, exit angles, etc.). The kinematic variables values along the design RETs were calculated “point by point” by MATLAB software to take into account nonuniform motion regimen. The obtained results show that both the Bloss curve and the multiparameter clothoid having a shape factor equal to 2 are capable of better contribution in terms of safety and comfort. Implications in the airport construction field are related to the possibility of using lower deceleration values compared to current standards, that is, allowing higher exit speed for the same deceleration. This allows aircrafts to vacate the runway more quickly and, therefore, to increase runway capacity without taking expensive RETs repositioning.

An apparatus to study arc-wire direct energy metal deposition additive manufacturing process in a drop tower microgravity platform.

Understanding the mechanisms and dynamics of molten metal droplet transfer within the plasma of a directed energy deposition arc process in microgravity is critical for optimizing the build process with minimal defects. This paper presents a unique experimental setup designed to investigate the transfer of molten metal droplets in the microgravity environment of a drop tower. The primary design of the apparatus revolves around accommodating, within the confines of the drop tower experimental capsule, essential components, including a high-speed camera with necessary filters for capturing molten metal droplets, a consumable electrode wire-arc setup, batteries, a linear traverse stage for single bead deposition, sensors, data acquisition systems, online communication systems, and the control system. These systems are secured to withstand the high deceleration forces at the end of a free fall in the drop tower. The arrangement has demonstrated consistent deposition outcomes, capturing clear images of droplet transfers using a high-speed camera along with voltage, current, and temperature data during the microgravity state induced by free fall. This apparatus will serve as a foundational element in establishing a viable additive manufacturing capability for space applications, as it provides fundamental insights into the transfer of molten metal droplets.

Design charts for hydraulic twister based aircraft arrester gear

In this article, arrestment of an aircraft by a hydraulic twister based system is modeled and reduced to simple design charts. We are primarily interested in performance parameters like maximum deceleration, run-out distance, and maximum tape force. We first present a simplified mechanical model for the system. Some analytical progress is possible with the governing nonlinear differential equation, yielding expressions for velocity and acceleration in terms of displacement. The system has only two nondimensional parameters. This allows us to present simple design charts for the performance parameters. The same approach is extended to secondary performance parameters namely maximum jerk and the time at which maximum deceleration occurs. We choose some practical parameter sets and demonstrate the use of our charts. These charts can be used for design calculations and quick performance prediction of an arresting gear design for different weight classes of aircraft and practical initial velocities.

Imaging in Whiplash-Associated Disorders.

"Whiplash," a term describing the severe acceleration and deceleration forces applied to the head, craniocervical junction (CCJ), and cervical spine during trauma, is one of the most frequent mechanisms of injury to the CCJ. The CCJ is a complex region at the transition of the cranium and the cervical spine, essential for maintaining craniocervical stability. In whiplash injuries, the CCJ may be compromised due to underlying ligamentous or, less frequently, osseous, intravertebral disk and/or muscular lesions. Imaging is crucial in detecting acute lesions but may also play a role in the follow-up of chronic pathology because soft tissue lesions and progressive disk pathology could contribute to a whiplash-associated disorder.

Repeat sprint fatigue and altered neuromuscular performance in recreationally trained basketball players.

The primary aim of the present study was to investigate how the fatigue induced through a repeat sprint protocol acutely affected different measures of neuromuscular performance. Recreationally trained basketball players (n = 25) volunteered to participate in the study, and performed three countermovement jumps (CMJ), as well as three drop jumps (DJ) prior to a fatiguing repeat sprint protocol. These procedures were repeated two minutes, and 15 minutes, following the protocol. Various force-time metrics were extracted from the jump tasks, and linear mixed models with subject ID as the random factor, and time as the fixed factor were used to investigate changes across the three time points. To account for the performance during the repeat sprint protocol, a second, two factor model was performed with time and repeat sprint ability (RSA) as the fixed factors. Study results indicated that the sample as a whole merely experienced fatigue-induced decreases in jump height from pre-repeat sprint ability protocol (pre-RSA) within the CMJ compared to two minutes post-repeat sprint ability protocol (post-RSA1) and 15 minutes post-repeat sprint ability protocol (post-RSA2), while jump height within the DJ was only significantly different from pre-RSA at post-RSA1. Further, despite the implementation of the fatiguing RSA protocol, over the course of the three time-points, participants seemed to perform the two jump tasks more efficiently, seen through significantly lower contraction times, greater eccentric (ECC) peak power, and greater ECC mean deceleration force within the CMJ following the RSA task. The two-factor model revealed that several significant time*RSA interactions were found for metrics such as ECC peak velocity and peak power in the CMJ, as well as reactive strength index in the DJ. This suggests that the level of RSA influenced changes across CMJ and DJ characteristics and should be accounted for when interpreting fatigue-induced changes in neuromuscular performance.

Reliability and sensitivity to change of post-match physical performance measures in elite youth soccer players.

To effectively monitor post-match changes in physical performance, valid, reliable and practical measures which are sensitive to change are required. This study aimed to quantify test-retest reliability and sensitivity to change of a range of physical performance measures recorded during an isometric posterior chain (IPC) lower-limb muscle test and a countermovement jump (CMJ) test. Eighteen Italian Serie A academy soccer players performed three IPC repetitions per limb and five CMJ trials in 4 testing sessions. Test-retest reliability was evaluated between two testing sessions seven days apart using typical error of measurement, coefficient of variation and intraclass correlation coefficient. Sensitivity to change was assessed on two additional testing sessions performed before and immediately after a soccer match through Hedges' g effect size (g) and comparisons to typical error. Absolute reliability (coefficient of variations) ranged from 1.5 to 8.8%. IPC and CMJ measures demonstrated moderate to excellent relative reliability (intraclass correlation coefficients ranged from 0.70 to 0.98). A wide range of physical performance measures showed significant alterations post-match (p < 0.05; g: small to moderate). IPC peak force and torque, CMJ reactive strength index modified, CMJ eccentric forces (mean breaking force, mean deceleration force, peak force, force at zero velocity) and CMJ mean power measures had post-match changes greater than their typical variation, demonstrating acceptable sensitivity in detecting performance changes at post-match. IPC peak force and torque, CMJ reactive strength index modified, CMJ eccentric phase forces and CMJ mean power were found to be both reliable and sensitive to change, and thus may be appropriate for monitoring post-match neuromuscular performance in youth soccer population.

Longitudinal Outcomes of Cumulative Impact Exposure on Oculomotor Functioning in Professional Motorsport Drivers

Professional motorsport drivers are regularly exposed to biomechanical forces comparable with those experienced by contact and collision sport athletes, and little is known about the potential short-term and long-term neurologic sequelae. To determine whether cumulative impact exposure is associated with oculomotor functioning in motorsport drivers from the INDYCAR professional open-wheel automobile racing series. This is a longitudinal retrospective cohort study conducted across 3 racing seasons (2017-2019). Statistical analyses were conducted in November 2021. Data were retrieved from a secondary care setting associated with the INDYCAR series. INDYCAR series drivers who participated in 3 professional level racing seasons and were involved in at least 1 contact incident (ie, crash) in 2 of the 3 seasons were included in the study. Cumulative acceleration and deceleration forces and total contact incidents (ie, crashes) measured via accident data recorder third generation chassis and ear accelerometers. Postseries oculomotor performance, including predictive saccades, vergence smooth pursuit, and optokinetic nystagmus, was measured annually with a head-mounted, clinical eye tracking system (Neurolign Dx 100). Thirteen drivers (mean [SD] age, 29.36 [7.82] years; all men) sustained median resultant acceleration forces of 38.15 g (observed range, 12.01-93.05 g; 95% CI, 30.62-65.81 g) across 81 crashes. A 2-way multivariate analysis of variance did not reveal a statistically significant association between ear and chassis average resultant g forces, total number of contact incidents, and racing season assessed (F9,12 = 0.955; P = .54; Wilks Λ = 0.44). In this cohort study of professional drivers from the INDYCAR series, there were no statistically significant associations among cumulative impact exposure, racing season assessed, and oculomotor performance. Longitudinal studies across racing seasons using multidimensional examination modalities (eg, neurocognitive testing, advanced imaging, biomarkers, and physical examination) are critical to understand potential neurological and neurobehavioral sequelae and long-term consequences of cumulative impact exposure.

Analytical Approach for Vehicle Body Structures Behaviour Under Crash at Aspects of Overloading and Crumple Zone Length

Abstract Road safety problem is still topical, especially since the number of vehicles and the volume of traffic are increasing. It is possible to increase the safety of road users through systemic changes in many areas related to transport. The deformation of the vehicle body during an accident has an impact on the loads acting on the passengers. Vehicle body deformation depends on complex parameters, and knowledge of these parameters is essential for designing crumple zones and the accident reconstruction process. Knowledge of the mechanical parameters of the vehicle structure during deformation is also a reference to passenger injury indicators assessment. This paper reports results from the analytical approach for determining the protection level of personal vehicles. The proposed conception is based on the results from the static stiffness characteristic of the Ford Taurus, which gives the possibility of phenomenological and simple body crumple analytical description at a speed equal to 10 km/h, 40 km/h, 56 km/h and 60 km/h, which is an original part of the work. The approach enables us to describe the vehicle crash by focusing on variations of deformation in time, stiffness, vehicle collision time (duration), deceleration and dynamic crash force. Basing on the body stiffness data of the personal vehicle, the length of the deformation zone in the front of the car and the maximum values of force at the crash for a speed of 60 km/h are presented. Results obtained by the authors show that is possible to estimate the overloading level during the crash time of a vehicle based on the stiffness characteristic of the car body. The proposed methodology can be developed and the advantage of the presented procedure is an uncomplicated useful tool for solving complex problems of a vehicle crash.

COUNTERMOVEMENT JUMP FORCE-TIME METRICS AND MAXIMAL HORIZONTAL DECELERATION PERFORMANCE IN PROFESSIONAL MALE BASKETBALL PLAYERS

Basketball is a sport that relies heavily on an athlete’s ability to rapidly decelerate in order to change direction, avoid a defender, or create space. Recent literature has proposed novel ways of measuring maximal horizontal deceleration using radar technology. The aim of this study was to investigate the relationships between different countermovement jump (CMJ) force-time characteristics and metrics related to maximal horizontal deceleration for a sample of professional male basketball players. To gain further insight into performance qualities that influence horizontal deceleration performance, athletes were separated into high- and low-performance groups for all horizontal deceleration metrics, using a median split analysis, and differences in CMJ force-time metrics were investigated between groups. The results revealed no significant correlations between any CMJ force-time metrics and horizontal deceleration performance. However, athletes’ height and body mass were correlated with different deceleration performance measures, such as average deceleration, horizontal deceleration impulse, and time to stop. Higher performing athletes with regards to average horizontal deceleration and horizontal braking impulse relative to body mass generated greater concentric power (effect size (ES) = 1.04, ES = 0.86) and concentric velocities (ES = 1.17, ES = 0.97), as well as greater jump heights (ES = 1.19, ES = 0.99). Reactive Strength Index modified values were also greater in the higher performing group for horizontal braking impulse relative to body mass (ES = 1.06). On the other hand, higher-performing athletes with regard to horizontal braking impulse generated greater eccentric deceleration force (ES = 0.81) and eccentric power values (ES = 0.88) in the CMJ. Findings may be of interest to practitioners physically preparing basketball players for the sport-specific deceleration actions they may encounter.

АНАЛИЗ ВЛИЯНИЯ РЕЖИМОВ ДВИЖЕНИЯ ЛЕСОВОЗНОГО ТЯГАЧА С ПОЛУПРИЦЕПОМ НА НАГРУЖЕННОСТЬ СЕДЕЛЬНО-СЦЕПНОГО УСТРОЙСТВА

The article presents the advantages of timber tractors with semi-trailers in comparison with single timber vehicles. The existing road condi-tions for the operation of saddle road trains in-volved in the transportation of timber to con-sumers are described. The causes and conse-quences of loading elements of saddle-coupling devices of road trains are considered. The de-pendences of the change in forces in the cou-pling device on the values of the coefficients of adhesion and the distribution of braking forces, the deceleration of the saddle road train, and also on the height of the center of gravity of the semi-trailer of the road train are presented. The regularities of changing the braking distance, deceleration and compression force in the fifth wheel coupling device of a road train due to un-derutilization of the coupling weight of a tractor with a semi-trailer are considered. The depend-ences of changes in loads in the fifth wheel cou-pling on road conditions, the load of the road train, the location of the fifth wheel coupling on the tractor, as well as on the damping coefficient are analyzed. An analysis of oscillograms of changes in forces in the pivot of the device in the process of sharp braking on a curvilinear and rectilinear trajectory with various options for braking by individual links is given. The influ-ence of the road train load, the speed of its movement, the type of road surface, the design parameters of the coupling device, the presence of lubricant on the base plate, the level of its wear on the change in the moment of resistance in such a device are described. The necessity of increasing the efficiency of timber tractors with semi-trailers by improving the existing designs of fifth wheel couplings is substantiated.

Enhanced-Dose Statins for ST-Segment Elevation Myocardial Infarction Patients after Emergency Percutaneous Coronary Intervention.

Background Acute ST-segment elevation myocardial infarction (STEMI) is a serious multiple acute cardiovascular disease. This study investigated the effect of statins on the efficacy and prognosis of STEMI patients after emergency PCI. Methods From October 2019 to January 2021, 98 patients with STEMI in our hospital were selected and divided into study group and control group. The study group took atorvastatin 40 mg 2 hours before surgery, 40 mg/day after surgery, and 20 mg/day 1 week later. The control group received 20 mg of atorvastatin every night after admission. The cardiac output, left ventricular ejection fraction, blood flow classification, vagus nerve function, heart rate deceleration force and chemoreflex sensitivity were compared between the two groups, and recorded the incidence of adverse reactions before and after treatment and 3 months after treatment. The number of major adverse cardiac events (MACEs) was also recorded. Results Before treatment, there were no differences in CO, CI, and LVEF between the study and control groups. After treatment, CO, CI, and LVEF in the study group were significantly higher than those in the control group. Before treatment, there was no significant difference in TIMI blood flow classification among the groups, and after treatment, the study group was better than the control group. DC and ChRS were significantly higher in the study group than in the control group. There was no difference in the incidence of adverse reactions between the study group and the control group. However, the incidence of MACE in the study group was lower than that in the control group. Conclusion Enhanced-dose atorvastatin for STEMI patients improved PCI treatment effect, cardiac function, and vagus nerve function and reduced the incidence of adverse cardiac events. Thus, statins are safe and worth considering.

AN ISOLATED MESENTERIC INJURY DUE TO BLUNT TRAUMA ABDOMEN CAUSINGGANGRENE OF SMALL BOWEL

Hollow viscous injury and mesenteric vascular injury after a blunt trauma abdomen although may be third most common injury , occurs only in 3 to 5 % of patients making it a rare entity. Significant mesentric injury includes disruption of mesenteric, active mesenteric bleeding, and mesenteric injury leading to gangrenous bowel.A 56 year old male was brought to the emergency room with history of road traffic accident with no external injuries.On presentation his vitals were stable , examination of abdomen revealed tense abdomen with guarding and rigidity. Given the hemodynamic stability of the patient CT scan of abdomen was done which revealed intraperitoneal free fluid , normal solid organs, abnormal bowel wall enhancement with extraluminal air pockets.Patient underwent emergency laparotomy to find out a massive hemoperitoneum with long segment gangrenous illeal bowel loop. Gangrenous bowel segment was resected and double barrel ileostomy was fashioned. The mechanism of injury involved is either direct compression forces or shearing and deceleration forces in Blunt trauma abdomen.Undiagnosed mesenteric injuries are associated with high morbidity and mortality rates due to life-threatening haemorrhage from disruption of mesenteric vessels, bowel infarction and peritonitis . This can be avoided by using imaging investigations af earliest and emergency surgical intervention.

Longitudinal whole-brain analysis of multi-subject diffusion data in diffuse axonal injury.

Diffuse axonal injury occurs with high acceleration and deceleration forces in traumatic brain injury (TBI). This lesion leads to disarrangement of the neuronal network, which can result in some degree of deficiency. The Extended Glasgow Outcome Scale (GOS-E) is the primary outcome instrument for the evaluation of TBI victims. Diffusion tensor imaging (DTI) assesses white matter (WM) microstructure based on the displacement distribution of water molecules. To investigate WM microstructure within the first year after TBI using DTI, the patient's clinical outcomes, and associations. We scanned 20 moderate and severe TBI victims at 2 months and 1 year after the event. Imaging processing was done with the FMRIB software library; we used the tract-based spatial statistics software yielding fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) for statistical analyses. We computed the average difference between the two measures across subjects and performed a one-sample t-test and threshold-free cluster enhancement, using a corrected p-value < 0.05. Clinical outcomes were evaluated with the GOS-E. We tested for associations between outcome measures and significant mean FA clusters. Significant clusters of altered FA were identified anatomically using the JHU WM atlas. We found increasing spotted areas of FA with time in the right brain hemisphere and left cerebellum. Extensive regions of increased MD, RD, and AD were observed. Patients presented an excellent overall recovery. There were no associations between FA and outcome scores, but we cannot exclude the existence of a small to moderate association.

Распыление атомов металлов кильватерным потенциалом, возбужденным пучком электронов

Abstract. The process of metal atoms sputtering during a corona discharge is considered. When an electron moves in a medium at some velocity, charge screening occurs with a delay in space and time, which leads to the emergence of a wake potential. The excited oscillations of the wake charge lead to the appearance of additional forces. The energy loss of a moving particle per unit path is determined by the work produced of the deceleration force that acts on the particle from the side of the wake potential it creates in the medium. The paper considers the effect of the wake potential on the ions (atoms) sputtering of the lattice matrix. A well-known expression is used for the wake potential excited by a charged particle moving with energy, greater than the Fermi energy. An expression for the sputtering cross-section of metal atoms under the action of the wake potential excited by the electron beam is obtained. It is shown that the result of sputtering does not depend on the charge sign of the incident particle (electron or ion).

Sputtering of metal atoms with the wake potential excited by an electron beam

The process of metal atoms sputtering during a corona discharge is considered. When an electron moves in a medium at some velocity, charge screening occurs with a delay in space and time, which leads to the emergence of a wake potential. The excited oscillations of the wake charge lead to the appearance of additional forces. The energy loss of a moving particle per unit path is determined by the work produced of the deceleration force that acts on the particle from the side of the wake potential it creates in the medium. The paper considers the effect of the wake potential on the ions (atoms) sputtering of the lattice matrix. A well-known expression is used for the wake potential excited by a charged particle moving with energy, greater than the Fermi energy. An expression for the sputtering cross-section of metal atoms under the action of the wake potential excited by the electron beam is obtained. It is shown that the result of sputtering does not depend on the charge sign of the incident particle (electron or ion). Keywords: corona discharge, nanoparticles, metal surface, inelastic scattering, wake potential.

A Comparative Study on the Temperature Effect of Solid Birch Wood and Solid Beech Wood under Impact Loading.

In order to use wood for structural and load-bearing purposes in mechanical engineering, basic information on the impact behaviour of the material over a wide temperature range is needed. Diffuse porous hardwoods such as solid birch wood (Betula pendula) and solid beech wood (Fagus sylvatica) are particularly suited for the production of engineered wood products (EWPs) such as laminated veneer lumber (LVL) or plywood due to their processability in a veneer peeling process. In the frame of this study, solid birch wood and solid beech wood samples (300 × 20 × 20 mm3) were characterised by means of an impact pendulum test setup (working capacity of 150 J) at five temperature levels, ranging from −30 °C to +90 °C. The pendulum hammer (mass = 15 kg) was equipped with an acceleration sensor in order to obtain the acceleration pulse and deceleration force besides the impact bending energy. In both solid birch wood and solid beech wood, the deceleration forces were highest at temperatures at and below zero. While the average impact bending energy for solid birch wood remained almost constant over the whole considered temperature range, it was far less stable and prone to higher scattering for solid beech wood.