Low Recoil Research Articles

Dynamics at conical intersections: The influence of O–H stretching vibrations on the photodissociation of phenol

Comparing the recoil energy distributions of the fragments from one-photon dissociation of phenol-d(5) with those from vibrationally mediated photodissociation shows that initial vibrational excitation strongly influences the disposal of energy into relative translation. The measurements use velocity map ion imaging to detect the H-atom fragments and determine the distribution of recoil energies. Dissociation of phenol-d(5) molecules with an initially excited O-H stretching vibration produces significantly more fragments with low recoil energies than does one-photon dissociation at the same total energy. The difference appears to come from the increased probability of adiabatic dissociation in which a vibrationally excited molecule passes around the conical intersection between the dissociative state and the ground state to produce electronically excited phenoxyl-d(5) radicals. The additional energy deposited in electronic excitation of the radical reduces the energy available for relative translation.

The time response of glass Resistive Plate Chambers to heavily ionizing particles

The HARP system of resistive plate chambers (RPCs) was designed toperform particle identification by the measurement of the difference in the time-of-flight of differentparticles. In previous papers an apparent discrepancy was shown between theresponse of the RPCs to minimum ionizing pions and heavily ionizingprotons. Using the kinematics of elastic scattering off a hydrogen target acontrolled beam of low momentum recoil protons was directed onto the RPCchambers. With this method the trajectory and momentum, and hence thetime-of-flight of the protons can be precisely predicted without needfor a measurement of momentum of the protons.It is demonstrated that the measurement of the time-of-arrival ofparticles by the thin gas-gap glass RPC system of the HARP experimentdepends on the primary ionization deposited by the particle in thedetector.

Two-channel scheme for dark matter particle detection based on a low-temperature magnetic calorimeter

Problems of dark matter (DM) particle detection are briefly reviewed. An original two-channel scheme for direct detection of cosmic DM particles is proposed. This scheme is based on a superlow-temperature calorimeter which includes a nuclear spin system whose magnetic response is measured by a quantum interferometer (SQUID). Low threshold and the capability for efficiently suppressing the recoil-electron background are the most important advantages of the proposed scheme. They make it possible to detect DM particles in the range of extremely low recoil energies and carry out direct DM search with high sensitivity.

Imaging the State-Specific Vibrational Predissociation of the C2H2−NH3Hydrogen-Bonded Dimer

The state-to-state vibrational predissociation (VP) dynamics of the hydrogen-bonded ammonia-acetylene dimer were studied following excitation in the asymmetric CH stretch. Velocity map imaging (VMI) and resonance-enhanced multiphoton ionization (REMPI) were used to determine pair-correlated product energy distributions. Following vibrational excitation of the asymmetric CH stretch fundamental, ammonia fragments were detected by 2 + 1 REMPI via the B1E'' <-- X1A1' and C'1A1' <-- X1A1' transitions. The fragments' center-of-mass (c.m.) translational energy distributions were determined from images of selected rotational levels of ammonia with one or two quanta in the symmetric bend (nu2 umbrella mode) and were converted to rotational-state distributions of the acetylene co-fragment. The latter is always generated with one or two quanta of bending excitation. All the distributions could be fit well when using a dimer dissociation energy of D0 = 900 +/- 10 cm(-1). Only channels with maximum translational energy <150 cm(-1) are observed. The rotational excitation in the ammonia fragments is modest and can be fit by temperatures of 150 +/- 50 and 50 +/- 20 K for 1nu2 and 2nu2, respectively. The rotational distributions in the acetylene co-fragment pair-correlated with specific rovibrational states of ammonia appear statistical as well. The vibrational-state distributions, however, show distinct state specificity among channels with low translational energy release. The predominant channel is NH3(1nu2) + C2H2(2nu4 or 1nu4 + 1nu5), where nu4 and nu5 are the trans- and cis-bend vibrations of acetylene, respectively. A second observed channel, with much lower population, is NH3(2nu2) + C2H2(1nu4). No products are generated in which the ammonia is in the vibrational ground state or the asymmetric bend (1nu4) state, nor is acetylene ever generated in the ground vibrational state or with CC stretch excitation. The angular momentum (AM) model of McCaffery and Marsh is used to estimate impact parameters in the internal collisions that give rise to the observed rotational distributions. These calculations show that dissociation takes place from bent geometries, which can also explain the propensity to excite fragment bending levels. The low recoil velocities associated with the observed channels facilitate energy exchange in the exit channel, which results in statistical-like fragment rotational distributions.

Absorbierbare Stents

Coronary stent implantation started in Germany 20 years ago. In the beginning, the progress was very slow and accelerated 10 years later. Meanwhile, coronary stent implantation is a standard procedure in interventional cardiology. From the beginning of permanent stent implantation, research started to provide temporary stenting of coronary arteries, first with catheter-based systems, later with stent-alone technology. Stents were produced from polymers or metal. The first polymer stent implantation failed except the Igaki-Tamai stent in Japan. Newly developed absorbable polymer stents seem to be very promising, as intravascular ultrasound (IVUS) and optical coherence tomography have demonstrated. Temporary metal stents were developed based on iron and magnesium. Currently, the iron stent is tested in peripheral arteries. The absorbable magnesium stent (Biotronik, Berlin, Germany) was tested in peripheral arteries below the knee and meanwhile in the multicenter international PROGRESS-AMS (Clinical Performance and Angiographic Results of Coronary Stenting with Absorbable Metal Stents) study. The first magnesium stent implantation was performed on July 30, 2004 after extended experimental testing in Essen. The magnesium stent behaved like a bare-metal stent with low recoil of 5-7%. The stent struts were absorbed when tested with IVUS. Stent struts were not visible by fluoroscopy or computed tomography (CT) as well as magnetic resonance imaging (MRI). That means, that the magnesium stent is invisible and therefore CT and MRI can be used for imaging of interventions. Only using micro-CT the stent struts were visible. The absorption process could be demonstrated in a patient 18 days after implantation due to suspected acute coronary syndrome, which was excluded. IVUS showed a nice open lumen. Stent struts were no longer visible, but replaced by tissue indicating the previous stent location. Coronary angiography after 4 months showed an ischemia-driven target lesion revascularization rate of 23.8% which was below the 30% cut point of the study protocol. No myocardial Q wave infarction or death were reported. The primary endpoint was reached. During the follow-up period, vasomotion was tested in some of the patients. The proof of principle was confirmed: restoration of vasomotion during acetylcholine testing. The development of the absorbable magnesium stent, which was pushed forward by B. Heublein, Hanover, Germany, has been successful and opens new possibilities for treatment of coronary arteries. Permanent foreign-body implantation is avoided allowing further revascularization procedures in the future, bypass grafting, and restoration of vasomotion. Even prophylactic stenting in nonsignificant stenosis, like vulnerable lesions, may become a regular procedure. Noninvasive coronary imaging by CT and MRI is now possible. Stenting of children and in peripheral arteries may become a standard procedure. Currently, the degradation process of the magnesium stent has to be prolonged, and the neointima proliferation rate has to be reduced so that the DREAM (Drug-Eluting Absorbable Magnesium Stent) concept of Ron Waksman, Washington, DC, USA, can be realized.

Charging of metal clusters in helium droplets exposed to intense femtosecond laser pulses

We review the strong field (10(13)-10(16) W cm(-2)) laser excitation of metal clusters (Cd(N), Ag(N) and Pb(N)) embedded in He nanodroplets. Plasmon enhanced ionization obtained by stretching the laser pulses to several hundreds of femtoseconds or by using dual pulses with a suitable optical delay leads to a Coulomb explosion of highly charged atomic ions. The charging dynamics can be well described by corresponding semiclassical Vlasov simulations. The influence of the He environment on the ionization process and on the final charge distribution is discussed. Evidence is found that He(2+) is generated in collisions with highly charged metal ions. In contrast, singly and doubly charged ions with low recoil energies induce the formation of He snowballs with a distinct shell structure around the ion. Laser intensity thresholds for snowball formation and for the ionization of clusters are investigated by applying intensity selective scanning.

Direct dark matter search using large-mass superheated droplet detectors in the PICASSO experiment

The PICASSO experiment investigates the presence and nature of dark matter in the Universe. The experiment is based on the detection of acoustic signals generated in explosive phase transitions induced by dark matter particles. This technique is an alternative more traditional detection technique like scintillation and ionisation, which are largely employed for dark matter search. One of the main advantages of this technique, besides its sensitivity to very low nuclear recoil energies (few keV), is its excellent background suppression features. A pilot experiment consisting of six superheated droplet detectors (40 g of active mass) is presently taking data at the Sudbury Neutrino Observatory (SNO) at a depth of 2000 m. We discuss the operation, calibration and data acquisition of the experiment and also the ongoing work to increase the sensitivity and the active mass of the detectors.

The Importance of Adult Literacy Issues in Social Work Practice

For many reasons, it is not uncommon for some clients to procrastinate, make excuses, or engage in noncompliant behavior in social work interactions. For some clients, however, these responses are an attempt to hide poor literacy skills. There are many indicators of the extent of low literacy in our nation. For example, according to the most recent national assessment of literacy skills, conducted in 2003, nearly 16 percent of the adult population reads and understands at a below basic level of literacy and has difficulty with daily functional reading tasks. Approximately 28 percent of the adult population is at the basic level of literacy and can only perform simple and everyday reading tasks. People with low literacy skills have difficulty with tasks such as identifying a location on a map and calculating the total costs of ordering supplies from a catalog (National Center for Education Statistics, n.d.). Other indicators come from sources such as the census. According to the 2000 Census, approximately 23 percent of adults in the United States did not graduate from high school or get a high school equivalency diploma (Lasater & Elliott, 2004). Even with a high school diploma, many individuals read three or four years below their highest grade of completion in school (Hochhauser, 1997). Twenty percent of the adults born in the United States and immigrants who speak English proficiently have only basic skills that are considered insufficient for the workplace (Comings, Reder, & Sum, 2001). When people with low literacy skills are asked about their ability to read, many report that they can read well. For example, according to reports of the National Adult Literacy Survey a high percentage (66 percent to 75 percent) of adults reading at the lowest literacy skill level described themselves as being able to read or very (Kirsch, Jungeblut, Jenkins, & Kolstad, 1993). Some adult learners in the study reported that they could read well because in their daily lives they are able to read what they need to get along and therefore do not realize how deficient their reading skills truly are. Others were simply providing socially desirable answers. Many individuals with low literacy recoil or become defensive at the mention of anything that might expose their literacy issues, and they often find complicated ways to hide their poor literacy skills. For example, we have worked with students who cannot tell time. Their employers do not realize that this is an issue because the students rely on environmental clues to help them get through the day. Specifically, in the morning, the beginning of a particular television show signals that it is time to leave the house; people leaving their offices in the middle of the day indicates that it is lunch time; and people leaving the office at the end of the day provides clues that the work day is done. Many people with low reading abilities are ashamed of their circumstances. In a study of patients in acute care at a large public hospital in Atlanta, Parikh and colleagues (1996) found that nearly 40 percent of individuals who reported having low literacy skills admitted their feelings of shame. Sixty-seven percent of their interviewees had never told their spouses, more than half had never told their children, relatives, or friends of their problems with reading and understanding what they read, and the vast majority had likewise never told coworkers or supervisors. Here's a typical scenario we encounter in the course of our work. Jane (pseudonym) is an unemployed 55-year-old African American woman who recognizes words at the 3.8 grade level and has attended our three-month adult literacy class. She completed the ninth grade and dropped out of school because she found it too difficult and was constantly embarrassed by her poor reading skills. Family members also encouraged her to drop out because they needed help taking care of her younger siblings. …

Dynamical Loading of the Muzzle Area of a Gun Barrel Including a Muzzle Brake

A modern tank gun for light vehicles should be light in weight and have a low recoil force. Therefore it needs an integrated muzzle brake that, however, reduces the strength in the muzzle area. The loading due to gas pressure in this area is as fast as the projectile, and some dynamical effects like traveling waves have to be taken into account. The analytical solution of traveling waves for a smooth tube will be explained on the basis of the shell theory for thin shells. The solution leads to a deeper understanding of the nature of these waves than a pure numerical solution. Since tubes are not really thin, even in the muzzle area, the error that may occur when applying the shell theory is estimated. The analytical solution will be compared to some finite element solutions, which include a multiperforated muzzle brake with a cover tube. The results give some useful hints to the interaction between gas pressure, projectile velocity, and wall thickness and help to reduce the weight of the barrel.

Flow Limitation in Liquid-Filled Lungs: Effects of Liquid Properties

Flow limitation in liquid-filled lungs is examined in intact rabbit experiments and a theoretical model. Flow limitation ("choked" flow) occurs when the expiratory flow reaches a maximum value and further increases in driving pressure do not increase the flow. In total liquid ventilation this is characterized by the sudden development of excessively negative airway pressures and airway collapse at the choke point. The occurrence of flow limitation limits the efficacy of total liquid ventilation by reducing the minute ventilation. In this paper we investigate the effects of liquid properties on flow limitation in liquid-filled lungs. It is found that the behavior of liquids with similar densities and viscosities can be quite different. The results of the theoretical model, which incorporates alveolar compliance and airway resistance, agrees qualitatively well with the experimental results. Lung compliance and airway resistance are shown to vary with the perfluorocarbon liquid used to fill the lungs. Surfactant is found to modify the interfacial tension between saline and perfluorocarbon, and surfactant activity at the interface of perfluorocarbon and the native aqueous lining of the lungs appears to induce hysteresis in pressure-volume curves for liquid-filled lungs. Ventilation with a liquid that results in low viscous resistance and high elastic recoil can reduce the amount of liquid remaining in the lungs when choke occurs, and, therefore, may be desirable for liquid ventilation.

Exclusive rareB→K*ℓ+ℓ−decays at low recoil: Controlling the long-distance effects

We present a model-independent description of the exclusive rare decays $\overline{B}\ensuremath{\rightarrow}{K}^{*}{e}^{+}{e}^{\ensuremath{-}}$ in the low recoil region (large lepton invariant mass ${q}^{2}\ensuremath{\sim}{m}_{b}^{2}$). In this region the long-distance effects from quark loops can be computed with the help of an operator product expansion in $1/Q$, with $Q={{m}_{b},\sqrt{{q}^{2}}}$. Nonperturbative effects up to and including terms suppressed by $\ensuremath{\Lambda}/Q$ and ${m}_{c}^{2}/{m}_{b}^{2}$ relative to the short-distance amplitude can be included in a model-independent way. Based on these results, we propose an improved method for determining the Cabibbo-Kobayashi-Maskawa matrix element $|{V}_{ub}|$ from a combination of rare and semileptonic $B$ and $D$ decays near the zero recoil point. The residual theoretical uncertainty from long-distance effects in this $|{V}_{ub}|$ determination comes from terms in the operator product expansion of order ${\ensuremath{\alpha}}_{s}(Q)\ensuremath{\Lambda}/{m}_{b}$, ${\ensuremath{\alpha}}_{s}^{2}(Q)$, ${m}_{c}^{4}/{m}_{b}^{4}$, and duality violations, and is estimated to be below 10%.

Reactor searches for neutrino magnetic moment as a probe of extra dimensions

We present calculations of the magnetic moment contribution to neutrino electron scattering in large extra dimension brane-bulk models (LED) with three bulk neutrinos. We discuss the cases with two and three large extra dimensions of sizes $R$. The calculations are done using reactor flux from Uranium, $^{235}\mathrm{U}$ as the neutrino source. We find that if the electron neutrino mass is chosen to be in the range of 1 eV, the differential cross section for $\overline{\ensuremath{\nu}}\ensuremath{-}e$ scattering for low electron recoil energy can be of the same order as the presently explored values in reactor experiments. Furthermore the spectral shape for the LED models is different from the four dimensional case. Future higher precision reactor experiments can therefore be used to provide new constraints on a class of large extra dimension theories.

Phase of the annual modulation as a tool for determining the mass of the weakly interacting massive particle

The count rate of weakly interacting massive particle (WIMP) dark matter candidates in direct detection experiments experiences an annual modulation due to the Earth's motion around the Sun. In the standard isothermal halo model, the signal peaks near June 2nd at high recoil energies; however, the signal experiences a phase reversal and peaks in December at low energy recoils. We show that this phase reversal may be used to determine the WIMP mass. If an annual modulation were observed with the usual phase (i.e., peaking on June 2nd) in the lowest accessible energy recoil bins of the DAMA, CDMS-II, CRESST-II, EDELWEISS-II, GENIUS-TF, ZEPLIN-II, XENON, or ZEPLIN-IV detectors, one could immediately place upper bounds on the WIMP mass of 103, 48, 6, 97, 10, 52, 29, and 29 GeV, respectively. In addition, detectors with adequate energy resolution and sufficiently low recoil energy thresholds may determine the crossover recoil energy at which the phase reverses, thereby obtaining an independent measurement of the WIMP mass. We study the capabilities of various detectors, and find that CRESST-II, ZEPLIN-II, and GENIUS-TF should be able to observe the phase reversal in a few years of runtime, and can thus determine the mass of the WIMP if it is $O(100\mathrm{GeV}).$ Xenon based detectors with 1000 kg (XENON and ZEPLIN-IV) and with energy recoil thresholds of a few keV require 25 kg yr exposure, which will be readily attained in upcoming experiments.

Temporal distortion of the annual modulation signal of weakly interacting massive particles at low recoil energies

We show that the main features of the annual modulation of the signal expected in a WIMP direct detection experiment, i.e., its sinusoidal dependence with time, the occurrence of its maxima and minima during the year and (under some circumstances) even the one-year period, are modified for anisotropic galactic halos. The most relevant effect is a peculiar distortion of the time-behaviour at low recoil energies for tangential anisotropies. The observation of these effects could provide a direct way of measuring (or setting limits on) the local degree of anisotropy of the velocity distribution of the dark matter particles.

Moving NRQCD for B form factors at high recoil

We derive the continuum and lattice tree-level moving NRQCD (mNRQCD) through order1/ m 2. mNRQCD is a generalization of NRQCD for dealing with hadrons with nonzero velocity u μ . The quark's total momentum is written as P μ = Mu μ + k μwherek μ ≪ Mu μ is discretized and Mu μ is treated exactly. Radiative corrections to couplings on the lattice are discussed. mNRQCD is particularly useful for calculating B → π and B → D form factors since errors are similar at low and high recoil.

Photodissociation of CFX=CHCl (X=H,F) at 193 nm by product translational spectroscopy

In this work, we have studied the photodissociation of CFX=CHCl (X=H,F) at 193 nm using product translational spectroscopy. Results show that while the photoelimination of fast Cl, slow Cl, HCl, and HF occurs for both molecules, the cleavage of the C=C bond is only measurable for CF2=CHCl. Among these, only the fast Cl product was detected with strong angular preference with respect to polarized laser light. Product translational energy distributions P(Et) were measured for all dissociation channels. The difference in the P(Et) distributions between three-centered (3C) and four-centered (4C) molecular elimination reactions was observed. The low recoil energy for 3C HCl elimination from CF2=CHCl strongly suggests that there is no concerted isomerization from :C=CF2 to FC≡CF. Although we detected no primary C–F bond fission in the present study, a relatively large yield of the secondary dissociation products F+C2H2 was determined for the internally excited fluorovinyl radical CHCHF. The results are discussed in terms of either a direct or an indirect dissociation process arising from excitation to the ππ* state, and comparisons between the title molecules are included.

2H(e,e(')p)n reaction at high recoil momenta.

The 2H(e,e(')p)n cross section was measured in Hall A of the Thomas Jefferson National Accelerator Facility near the top of the quasielastic peak (x(Bj)=0.964) at a four-momentum transfer squared, Q(2)=0.665 (GeV/c) (2) (omega=0.368 GeV, W=2.057 GeV), and for recoil momenta up to 550 MeV/c. The measured cross section deviates by 1-2sigma from a state-of-the-art calculation at low recoil momenta. At high recoil momenta the cross section is well described by the same calculation; however, in this region, final-state interactions and interaction currents are predicted to be large, and alternative choices of nucleon-nucleon potential and nucleon current operator may result in significant spread in the calculations.

Measurements of scintillation efficiency and pulse shape for low energy recoils in liquid xenon

Results of observations of low energy nuclear and electron recoil events in liquid xenon scintillator detectors are given. The relative scintillation efficiency for nuclear recoils is 0.22 +/- 0.01 in the recoil energy range 40 keV - 70 keV. Under the assumption of a single dominant decay component to the scintillation pulse-shape the log-normal mean parameter T0 of the maximum likelihood estimator of the decay time constant for 6 keV < Eee < 30 keV nuclear recoil events is equal to 21.0 ns +/- 0.5 ns. It is observed that for electron recoils T0 rises slowly with energy, having a value ~ 30 ns at Eee ~ 15 keV. Electron and nuclear recoil pulse-shapes are found to be well fitted by single exponential functions although some evidence is found for a double exponential form for the nuclear recoil pulse-shape.

High resolution measurement of the16O(γ,pn)14N0,1,2,…reaction

The exclusive ${}^{16}\mathrm{O}(\ensuremath{\gamma}{,pn)}^{14}{\mathrm{N}}_{0,1,2,\dots{}}$ reaction was measured for the photon energy range ${E}_{\ensuremath{\gamma}}=98.5$ to 141.0 MeV with an excitation energy resolution of 2.8 MeV. Protons were detected at $76\ifmmode^\circ\else\textdegree\fi{}$ and $82\ifmmode^\circ\else\textdegree\fi{}$ and coincident neutrons were detected at the opening angle for quasifree deuteron photodisintegration. Only the $T=0,$ ${1}^{+},$ 3.95 MeV state in the residual ${}^{14}\mathrm{N}$ nucleus was significantly populated. This corresponds to a preferred $L=0$ angular momentum transfer to the recoil nucleus as is expected for quasifree kinematics. The absence of significant population to other discrete states is evidence that absorption on correlated proton-neutron pairs with an angular momentum transfer of $L&gt;~2$ is largely suppressed for the low recoil momentum range of the current measurement. As a consequence of this fact, and the absence of unnatural parity states, only absorption on proton-neutron pairs in relative motion $l=0,2$ is expected for all possible shell model couplings. No significant population of the $T=1$ state at 2.31 MeV is consistent with previous measurements, demonstrating that absorption on proton-neutron pairs in an isospin triplet is suppressed. The results of the measurement to discrete states in the residual ${}^{14}\mathrm{N}$ nucleus are compared to microscopic calculations which include contributions above that of the mean field due to the short range and tensor parts of the nuclear potential. Clear separation in the contribution of ${(1p)}^{\ensuremath{-}2}$ and ${(1p)}^{\ensuremath{-}1}{(1s)}^{\ensuremath{-}1}$ proton-neutron pairs is seen to occur at an excitation energy of $20\ifmmode\pm\else\textpm\fi{}2 \mathrm{MeV}.$ Significant population of the ${(1p)}^{\ensuremath{-}1}{(1s)}^{\ensuremath{-}1}$ continuum above 20 MeV indicates that absorption on $L=1$ nucleon pairs is also important near quasifree kinematics.

Determination of H recoil cross-sections for He ions incident at 2.5–4.5 MeV and recoil angles from 30° to 60°

Proton differential recoil cross-sections were measured for impact of He ions in the energy range from 2.5 to 4.5 MeV and for recoil angles from 30° to 60°. For the first time, H recoil cross-sections at angles from 45° to 60° are reported. All the measured cross-sections, except those for 60°, deviate from the Rutherford cross-sections. Thin melamine foils (∼50 μg/cm 2) evaporated on ∼50 μg/cm 2 thick Cu were prepared as targets. Two surface barrier detectors positioned at forward angles were used to detect the recoiled and scattered atoms. One detector was kept all the time at 40° and was used to measure the loss of H due to irradiation. The experimental results were compared with the other available experimental data for lower recoil angles and a good agreement is found. A comparison is also made with the theoretical calculations obtained by fitting the phase shifts of the kinematic inverse reaction using the principle of detailed balance. Again an agreement is found for low recoil angles, but for 55° and 60° the experimental cross-sections are significantly smaller than the theoretical values.