Large Amount Of Kinetic Energy Research Articles

Exploring the Time Scales of H-Atom Elimination from Photoexcited Indole

Recent spectroscopic measurements have shown that following excitation of indole molecules above the (1)pipi*-(1)pisigma* conical intersection, photoinduced N-H bond cleavage results in a range of H-atom kinetic energy release. H-atoms with large amounts of kinetic energy were attributed to direct dissociation whereas those with low kinetic energy were attributed to indirect pathways such as statistical unimolecular decay. With use of a combination of femtosecond pump-probe spectroscopy and velocity map ion-imaging techniques, both energy and time-resolved photoinduced H-atom elimination at 200 nm has been measured. The results show that H-atoms with both high and low kinetic energies are generated on an ultrafast time scale, <200 fs, suggesting that on the time frame of our measurements (<200 ps) there appears to be a direct route to H-atom formation yielding H-atoms with low kinetic energies.

Intramolecular energy transfer and the driving mechanisms for large-amplitude collective motions of clusters

This paper uncovers novel and specific dynamical mechanisms that initiate large-amplitude collective motions in polyatomic molecules. These mechanisms are understood in terms of intramolecular energy transfer between modes and driving forces. Structural transition dynamics of a six-atom cluster between a symmetric and an elongated isomer is highlighted as an illustrative example of what is a general message. First, we introduce a general method of hyperspherical mode analysis to analyze the energy transfer among internal modes of polyatomic molecules. In this method, the (3n-6) internal modes of an n-atom molecule are classified generally into three coarse level gyration-radius modes, three fine level twisting modes, and (3n-12) fine level shearing modes. We show that a large amount of kinetic energy flows into the gyration-radius modes when the cluster undergoes structural transitions by changing its mass distribution. Based on this fact, we construct a reactive mode as a linear combination of the three gyration-radius modes. It is shown that before the reactive mode acquires a large amount of kinetic energy, activation or inactivation of the twisting modes, depending on the geometry of the isomer, plays crucial roles for the onset of a structural transition. Specifically, in a symmetric isomer with a spherical mass distribution, activation of specific twisting modes drives the structural transition into an elongated isomer by inducing a strong internal centrifugal force, which has the effect of elongating the mass distribution of the system. On the other hand, in an elongated isomer, inactivation of specific twisting modes initiates the structural transition into a symmetric isomer with lower potential energy by suppressing the elongation effect of the internal centrifugal force and making the effects of the potential force dominant. This driving mechanism for reactions as well as the present method of hyperspherical mode analysis should be widely applicable to molecular reactions in which a system changes its overall mass distribution in a significant way.

Subtalar dislocation: rare and often forgotten

A 17-year-old boy presented to the emergency department (ED) with pain and ankle deformity following an inversion injury during a basketball game. Radiographs of the right ankle (Fig. 1) showed loss of talonavicular alignment (white arrow) and widening of the talocalcaneal joint (black arrows). Furthermore, the midfoot was medially displaced in relation to the ankle (curved arrow). The findings are consistent with medial subtalar dislocation. Following failed manipulation and reduction (M&R) in the ED, successful closed M&R was achieved under general anaesthesia. Fig. 1 Radiographs of the right ankle showed loss of talonavicular alignment (white arrow) and widening of the talocalcaneal joint (black arrows). The midfoot was medially displaced in relation to the ankle (curved arrow) Medial subtalar dislocation is a rare dislocation and is not commonly seen as a sports injury as it requires transfer of a large amount of kinetic energy [1]. The weaker talocalcaneal and talonavicular ligaments often bear the brunt of the energy and are more commonly disrupted, compared to the relatively stronger calcaneonavicular ligament. Due to the high energy nature, up to 40% of dislocations are associated with open injury or have significant internal soft tissue injury related to ligament disruption. Clinically, it is important to recognize the midfoot deformity, and the foot is typically supinated and held in plantar flexion. This uncommon midfoot deformity is often not appreciated and standard ankle radiographs are performed. Nevertheless, prompt M&R prior to imaging should be attempted in all ankle injuries with significant deformity, as there is a high risk of neurovascular compromise [2]. Careful assessment and documentation of the overlying skin condition and distal neurovascular status are essential both in the acute and post-M&R period as skin necrosis as well as neurovascular injury can occur as a result of the initial injury or the M&R. Ankle radiographs, if performed, appear deceptively normal as the ankle joint remains intact. Careful scrutiny of the talonavicular and talocalcaneal joints is crucial for correct diagnosis. Long-term sequelae include talar avascular necrosis [3] and osteochondral fracture [4], as well as chronic instability and pain. Urgent reduction is important, and closed reduction under general anaesthesia is usually successful, often facilitated by keeping the knee in flexion to relax the gastrocnemius muscle. However, the capsule of the talonavicular joint and the extensor digitorum brevis tendon often block reduction and open reduction will then be necessary.

The Energy-Absorbing Characteristics of Tubular Structures With Geometric and Material Modifications: An Overview

For better crashworthiness performance, vehicles must protect its occupants by maintaining structural integrity and converting the large amount of kinetic energy into other forms of energy in a controllable and predictable manner in a crash situation. In doing so, lower crushing force would provide better safety for the vehicle occupants. This paper reviews the axial response of “modified” tubular sections with imperfections and fillers subjected to axial impact loads relevant to the field of structural crashworthiness. The use of imperfections sets the mode and initiation of collapse of a tube at a specific location and reduces the maximum crush force, hence improving the energy-absorbing characteristics of tubular structures. The types of imperfections discussed include prebuckle, parallel and dished indentations, cutouts, stiffeners, fillers, and wrapping.

Modelling the onset of oxide formation on metal surfaces from first principles

AbstractThe formation of ultrathin oxide layers on metal surfaces is a non-thermally-activated process which takes place spontaneously at very low temperatures within nanoseconds. This paper reports mechanistic details of the initial oxidation of bare metal surfaces, in particular Al(111) and TiN(001), as obtained by means of first-principles molecular dynamics modelling within the Density-Functional Theory. It is shown that the reactions of bare metal surfaces with O molecules take place according to a “hot-atom” dissociative mechanism which is triggered by the filling of the σ* antibonding molecular orbital and is characterised by a sudden release of a large amount of kinetic energy. This released energy provides a driving force for metal/oxygen place-exchange processes which are responsible for the onset of oxide formation at virtually 0 K and at oxygen coverages well below 1 monolayer (ML). Further simulations of the oxidation reactions reveal that a disordered ultrathin oxide forms on Al(111), whereas a rather ordered structure develops on TiN(001) following a selective oxidation process which leaves clusters of Ti vacancies in the TiN lattice underneath the oxide layer.

Flow burst‐induced Kelvin‐Helmholtz waves in the terrestrial magnetotail

The Kelvin‐Helmholtz instability (KHI) on the boundary of a flow channel in the Earth's plasma sheet is investigated using Cluster and Double Star TC1 data. It is shown that when Cluster moves into the flow channel the magnetometer measures strong oscillations of the magnetic field, that increase as the spacecraft move further into the flow channel. These waves are identified as Kelvin Helmholtz waves. DoubleStar TC1, closer to the Earth, also observes these waves when entering the flow channel but at larger amplitude and with only little flow. The increase in wave amplitude agrees with the KHI wave growth. It is argued that the development of the KHI can play a major rôle in flow braking in the magnetotail, which is an important aspect of magnetotail dynamics. The large amount of kinetic energy released by a reconnection event or bursty bulk flow gets converted to other kinds of energy such that in the near Earth region the flow is stopped.

Characteristics of Development

Two-component development systems using magnetic carriers and tribocharged toner particles are well established in electrophotography for high-quality development of electrostatic latent images at high speed. Two main approaches are used for these systems: development utilizing fixed magnets within a rotating developer roller, or development with a moving magnetic field, usually produced by a developer roller with a rotating magnetic core as well as a rotating outer surface or shell. The magnetic field from the rotating magnetic core provides a large amount of kinetic energy to the carrier and the toner particles moving toward the electrostatic latent image. Development to completion has been obtained with a rotating magnetic core development system. Completion is characterized by proportionality between the cube of the toner-charge-to-mass ratio, Q/m, and the voltage to completion, Vc, which is the difference between the developer bias and the voltage of the developed image.

Particle Image Velocimetry Measurements of the Three-Dimensional Flow in an Exhaust Hood Model of a Low-Pressure Steam Turbine

The three-dimensional flow structure inside an exhaust hood model of a low-pressure steam turbine was investigated using a particle image velocimetry (PIV) velocity field measurement technique. The PIV measurements were carried out in several selected planes under design operation conditions with simulated total pressure distribution and axial velocity profile. The mean flow fields revealed a complicated vortical flow structure and the major sources of energy loss. Vortices with different scales were observed inside the exhaust hood: a strong separation vortex (SV) behind the tip of the guide vane, a longitudinal vortex (LV) at the exhaust hood top, a large-scale passage vortex (PV) evolving throughout the flow path, and an end-wall vortex (EWV) in the region adjacent to the front end-wall. Both the SV and the large-scale PV seemed to consume large amounts of kinetic energy and reduce the pressure recovery ability. The results indicate that the steam guide vane and the bearing cone should be carefully designed so as to control the vortical flow structure inside the exhaust hood.

Long-term remnant evolution of compact binary mergers

We investigate the long-term evolution and observability of remnants originating from the merger of compact binary systems and discuss the differences to supernova remnants. Compact binary mergers expel much smaller amounts of mass at much higher velocities, as compared to supernovae and therefore the free expansion phase of the remnant will be short (∼1-10 yr). But merger events with high mass ejection exploding in a low density environment remain in this ejecta dominated stage for several hundred years and in general the remnants will be observable for a considerable time ( 10 6 - 10 7 yr). Events releasing large amounts of kinetic energy may be responsible for a subsample of observed giant HI holes of unknown origin as compact binaries merge far away from star forming regions. If the ejecta consist primarily of actinides, on long timescales the expelled material will contain mainly the few quasi-stable nuclei in the actinides range. Consequently the abundance of each isotope in the ejecta might be of the order of a few percent. During their decay some actinides will produce observational signatures in form of gamma ray lines. We particularly investigate the gamma ray emission of Am 243, Cm 247, Cm 248 and Bi 208 and estimate their observability in nearby remnants. Detections of the gamma ray lines with INTEGRAL will be possible only in very advantageous cases but these remnants are promising targets for future instruments using focusing optics for soft gamma rays. Due to the low mass expelled in mergers and due to the lack of free electrons in the ejecta, the merger remnants might be significantly fainter in bremsstrahlung and synchrotron radiation than comparable supernova remnants. Hence merger remnants might represent a candidate for very recently discovered dark accelerators which are hard gamma ray sources with no apparent emission in other bands.

Photon energy dependence of fragmentation of small argon clusters

Photofragmentation of small argon clusters with size below ten atoms is reported. In this size range significant modifications from the electronic properties and geometry take place. When tuning the photon energy through the argon 2p edge, the fragmentation pattern is changed. Specifically, cation dimer production is enhanced at the 2p(32)-->4s resonance, while above the 2p edge almost complete atomization is observed. In both cases, the widths of the peaks in the mass spectra indicate that a large amount of kinetic energy is imparted to the fragment due to the formation of multiply charged clusters. A model based on "Coulomb explosion"-charge separation, simply resulting in a complete atomization of the cluster with no dependence on the photon energy-is insufficient to explain the observed photofragmentation of small clusters.

Disorder‐induced heating of ultracold plasmas

AbstractWe report calculations for the disorder‐induced heating of the ions in ultracold plasmas that were created by ionization of ultracold, trapped gases. Since the ions gain a large amount of kinetic energy while building up negative potential energy, plasmas are usually heated to a moderately coupled state that is almost independent of the initial temperature. We show how this process is related to the establishment of Coulomb structure in the final plasma state. Several possibilities for reducing the heating by the introduction of structure in the initial state, i.e., the gas before ionization, are then discussed. (© 2003 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Comparison of methyl and hydroxyl protons generated in a Coulomb explosion event: application of a time-of-flight gating technique to methanol clusters

A time-of-flight (TOF) mass spectrometry gating technique is applied to a study of methanol clusters subjected to ionizations via intense femtosecond laser pulses. The resulting high charged species (C 2+, C 3+/O 4+) acquire large amounts of kinetic energy resulting from Coulomb repulsion of multicharged atomic ions that reside in close proximity to one another. Protons which are of two kinds, methyl and hydroxyl, also acquire large amounts of kinetic energy. When compared with protons generated from the Coulomb explosion of water clusters ((H 2O) n , n≤20), protons from methanol clusters ((CH 3OH) n , n≤10) acquire less overall average kinetic energy, which is in agreement with earlier findings that suggest greater clustering yields higher energy. Interestingly, despite the lower average kinetic energy released, the methanol protons peak at a higher value of energy than those generated in the water cluster system, an effect attributed to the presence of both methyl and hydroxyl groups.

Understanding 26Al Emission from Cygnus

The COMPTEL observations of the galactic 1.809 MeV emission attributed to the radioactive decay of 26Al have confirmed the diffuse nature of this interstellar emission line. One of the most significant features of the reconstructed intensity pattern is a flux enhancement towards Cygnus. This region is fairly young and contains a wealth of massive stars, most of them grouped in the Cygnus OB associations. Multi-frequency model fitting strongly supports the hypothesis of massive stars and their descendent supernovae being the dominant sources of interstellar 26Al as observed by COMPTEL. Massive stars and supernovae are known to impart a large amount of kinetic energy into their surroundings causing shock regions and large cavities in the ISM. In addition, a significant fraction of the electro-magnetic radiation of these stars is emitted in the EUV regime leading to photoionisation of the surrounding medium. We applied a population synthesis model in combination with an 1D model of expanding superbubbles to the Cygnus OB associations. Besides the expected 1.809 MeV flux and the γ-ray line intensity due to interstellar 60Fe we compute the sizes and expansion parameters of the expected HI-structures and the free–free emission intensities due to the photoionizing radiation from massive stars within this region of the sky. We discuss our present understanding of the Cygnus region with respect to the massive star census. Our model assigns about 70% of the 1.809 MeV intensity to six known OB associations, about 20% to known isolated sources and roughly 10% to an unknown diffuse component.

Influence of Compressor Exit Conditions on Combustor Annular Diffusers, Part 1: Diffuser Performance

In gas-turbine engines, the velocity of air issuing from the compressor must be reduced to permit effective operation of the downstream combustor. This is partly achieved by locating an annular diffuserbehind the compressor outlet guide vanes (OGV) and, in modern systems, the inlet of this diffuser is usually located at the trailing edge of the blade row. The interactions that occur between these components and, in particular, the impact on the measured diffuser performance are studied. A mainly experimental investigation has been undertaken in a fully annular facility that incorporates a single-stage axial-e ow compressor and simulated e ame tube. In addition, a constant-area passage, or diffusers of area ratio 1.45 or 1.60, can be incorporated immediately downstream of the OGV row. The results indicate that, within experimental error, the diffusers have little effect on the e ow within the OGVbladepassages. However,theOGV blade rowproducesa proe lethat, duemainly to thebladewakes,contains a relatively large amount of kinetic energy. Hence, even within the downstream constant area passage a signie cant pressure rise is observed as these wakes mix out. Additional pressure forces are introduced with the downstream diffusers present, but analysis of the experimental data indicates these have a limited effect on the wake mixing process, both in terms of stagnation pressure loss and static pressure rise. Hence, the overall static pressure rise measured, between the inlet and exit of each diffuser, is greater than that predicted using design charts obtained using more conventional axisymmetric inlet conditions. This cone rms previous work where it was thought that wake mixing can enhance diffuser performance.

Disks, Microjets, Windblown Bubbles, and Outflows in the Orion Nebula

New deep narrowband images of the Orion Nebula obtained with WFPC2 on the Hubble Space Telescope (HST) and spectra taken with the HIRES spectrometer at the Keck Observatory are presented. We report eight new circumstellar disks seen in silhouette against the background nebular light and about 30 dark disks embedded within the bright proplyds rimmed by ionization fronts. Deep narrowband λ6300 A images reveal skins of glowing [O I] emission associated with several disks embedded within bright proplyds. [O I] emission also surrounds one dark disk not surrounded by an ionization front; this object may be embedded within the photon-dominated, mostly neutral region behind the ionization front of the Orion Nebula. The intensity and morphology of the [O I] emission provides support for the photon-dominated–region models of externally irradiated circumstellar disks in which soft UV powers photoablation of the disk surface. Dozens of outflows powered by young stars have been discovered on the new images. More than 20 stellar jets emerge from the externally irradiated circumstellar disks or their associated young stars embedded within the Nebula. Most are one-sided (monopolar) subarcsecond-scale microjets, too small to be seen on ground-based images against the bright background nebular light. Additionally, wide-angle winds from 10 young stars in the outskirts of the Nebula power large-scale bow shocks facing the Trapezium OB stars. These shocks may be produced by wind-wind interactions where the T-Tauri winds interact with the outflow of plasma from the core of M42. The largest such structure, associated with the star LL Ori, contains a number of compact high–proper-motion clumps moving almost tangentially to the bow shock. The new data are combined with older HST images to determine proper motions for many nebular features. Neither the LL Ori type bow shocks in the outskirts of the nebula nor the Hα + [O III] arcs that surround many proplyds near the Trapezium show measurable proper motions and are therefore stationary structures. However, most other bow-shaped features not centered on young stars exhibit large proper motions, with velocities ranging from 50 to 300 km s-1. The sources of many of these moving features remain unknown. The proper-motion survey of the nebular core reveals the presence of about a dozen new large-scale (>0.1 pc) outflow complexes. Many of these new outflows originate from the vicinity of the high-luminosity OMC-1S infrared and submillimeter source complex located southwest of the Trapezium. These supersonic features provide evidence that stellar outflows inject large amounts of kinetic energy into the nebula. However, a quantitative analysis indicates that their total power is small compared with the power in the plasma flowing away from the main nebular ionization front.

Response of the Sphere Wake to Freestream Fluctuations

Direct numerical simulations have been used to investigate the response of the wake of a sphere to freestream fluctuations. This study has been motivated by the need to understand particle-induced turbulence enhancement in particulate flows. A sequence of simulations of flow past a sphere have been carried out where the frequency and amplitude of the freestream fluctuations and the flow Reynolds number has been varied systematically. It has been suggested that turbulence enhancement is primarily caused by vortex shedding from particles (Gore and Crowe, 1989; Hetsroni, 1989). Our simulations of the forced wake indicate that turbulence enhancement may be attributed to natural vortex shedding only when the freestream fluctuation level is low and the Reynolds number is greater than about 300. In addition to natural vortex shedding, the current simulations also suggest another mechanism for turbulence enhancement. It is found that in the presence of freestream fluctuations, the wake behaves like an oscillator and returns large amounts of kinetic energy to the surrounding fluid at resonance. This mechanism is not associated with natural vortex shedding and is therefore capable of enhancing freestream turbulence even at Reynolds numbers less than 300. Simulations also indicate that when the turbulence intensity of the carrier fluid is high, this resonance mechanism might be solely responsible for turbulence enhancement. Finally, our simulations also suggest a possible explanation for the correlation between turbulence enhancement and the ratio of the particle size to the size of energy containing eddies of turbulence found by Gore and Crowe (1989).

Dissociation dynamics of propargyl chloride molecular ion near the reaction threshold: manifestation of quantum mechanical tunneling

The Cl loss from the propargyl chloride molecular ion has been investigated using mass-analyzed ion kinetic energy spectrometry (MIKES). The kinetic energy release distribution in the unimolecular dissociation has been determined. The potential energy surface for the mechanistic pathway has been calculated at the B3LYP/6-311G** density functional theory level. The calculated potential energy surface suggested that the threshold dissociation of the propargyl chloride molecular ion produces the C(3)H(3)(+) ion, only with the cyclopropenium structure, and with the release of a large amount of kinetic energy. This is in agreement with experimental results. Also, calculation of the rate constants with statistical rate models predicted that the reaction observed on a microsecond time scale occurs via tunneling through the rate-determining isomerization barrier for H-atom transfer. It has been found that a broad lifetime distribution is a manifestation of quantum mechanical tunneling of a precursor prepared under thermal conditions. Reinterpretation of previous photoelectron-photoion coincidence results taking into account the tunneling effect necessitated raising the critical energy to 0.64 eV from the energy of 0.34 eV reported previously. Copyright 2000 John Wiley & Sons, Ltd.

Development of a Flared Energy-Absorbing Terminal for W-Beam Guardrails

A new flared W-beam guardrail terminal that incorporates energy-absorbing technology has been developed and successfully crash tested to meet the criteria presented in NCHRP Report 350. The terminal, designated FLEAT-350, incorporates an impact head designed to dissipate impact energy by producing a series of plastic hinges in the W-beam as the impact head is pushed down the guardrail. The energy-absorption mechanism allows the flared terminal to absorb large amounts of kinetic energy before the vehicle is allowed to gate through the system. Most components of the new terminal are similar to those incorporated in the SKT-350 terminal. The terminal system is 11.4 m (37.5 ft) long and incorporates a straight flare with a final end offset of between 0.76 m (2.5 ft) and 1.2 m (4 ft). The terminal uses two breakaway posts in foundation tubes and five rough-cut controlled-release terminal posts of 150 by 200 mm (6 by 8 in.). The energy-absorbing design minimizes problems associated with vehicles that penetrate the terminal and strike slopes, ditches, or other hazards behind the guardrail while still traveling at a high rate of speed. Furthermore the new design has fewer components and is less sensitive to post location and installation details than some other flared systems.

The production of NO by hypersonic flight

Behind the shock waves occurring during hypersonic flight, a large amount of kinetic energy is transformed into energy of the translational and rotational degrees of freedom of the molecules. For high Mach numbers temperatures of many thousand degrees may be reached immediately behind the shock front. Chemical reactions take place and nitric oxide is produced. For hypersonic aircraft the NO-production of the engines exceeds the nitric oxide production behind the shock wave as well as the NO-production in the boundary layers. Reentry vehicles entering into the earth’s atmosphere with high Mach numbers cause strong detached shock waves. For the Space Transfer Shuttle (STS) the NO-concentration in the wake averaged over a cross section of 10 6 m 2 is up to 800 times higher than the background NO-concentration. In total, an amount of about 5000 kg NO is produced for each shuttle descent; nitric oxide is formed in the altitude range 50 km<h<70 km . At current space activities this amount is rather small compared with natural sources of NO.

Development of a 100-km/h Reusable High-Molecular Weight/High-Density Polyethylene Truck-Mounted Attenuator

A reusable truck-mounted attenuator has been developed that dissipates kinetic energy through the lateral deformation of a nested cluster of high-molecular weight/high-density polyethylene cylinders. This 100-km/h impact attenuation device, called the Vanderbilt truck-mounted attenuator (VTMA), satisfies the crash testing requirements of NCHRP Report 350. It has been approved by the Federal Highway Administration for use on the national highway system under these NCHRP Report 350 guidelines. Most impact attenuation devices currently employed require the replacement of damaged structural components and spent-energy-dissipating elements following an impact event. Until these repairs and refurbishments are carried out, these safety devices are largely ineffective because they are unable to dissipate kinetic energy in a subsequent impact in an acceptable manner such that relevant occupant risk parameters are within prescribed limits. The VTMA is a reusable and self-restorative truck-mounted attenuator. It can dissipate large amounts of kinetic energy, undergo significant deformations and strains without fracturing, and then, essentially, regain its original shape and energy-dissipation potential on removal of the load. The VTMA design was optimized through finite-element modeling using DYNA3D. This inexpensive modeling tool resulted in a reduction in the number of expensive full-scale crash tests required to develop the system. Computer modeling can optimize the probability for success of a given full-scale crash test, removing the trial-and-error approach to appurtenance design.