Search

JYFLTRAP is a Penning trap system at the accelerator laboratory in Jyväskylä, Finland that enables high-precision experiments with stored, exotic species that are produced at the IGISOL facility. On one hand, these can be performed within the trap itself, like e.g. mass spectrometry. On the other hand, the trap can be used to provide the highly purified species for further experiments, e.g. for trap-assisted nuclear decay spectroscopy. This contribution focuses on these two possible applications with the presentation of some recent results on superallowed beta decays. [ABSTRACT FROM AUTHOR]

The masses of 80, 81, 82, 83Y, 83, 84, 85, 86, 88Zr and 85, 86, 87, 88Nb have been measured with a typical precision of 7keV by using the Penning trap setup at IGISOL. The mass of 84Zr has been measured for the first time. These precise mass measurements have improved Sp and QEC values for astrophysically important nuclides. [ABSTRACT FROM AUTHOR]

Abstract: Multiply charged ions of stable xenon isotopes from a plasma ion source have been mass-selected by the on-line mass separator ISOLDE/CERN and delivered to the triple-trap mass spectrometer ISOLTRAP. The doubly charged ions that survived the charge-exchange processes during bunching and ion preparation were transferred to a precision Penning trap for mass determination. Mass values were obtained for the isotopes with mass numbers . They are consistent with previous results except for the case of where a significant deviation from the literature value was found. The performance of ISOLTRAP is analyzed with respect to a future application of highly charged ions for mass determination of short-lived radionuclides at ISOLDE. [Copyright &y& Elsevier]

A Penning trap has been installed for isobaric beam purification at the IGISOL-facility at the University of Jyväskylä. In this paper, the technical details of this new device together with results of the first tests are presented. The mass resolving power, depending on the excitation parameters and the ion species, can be as high as 145 000 and the total transmission has been determined to be 17%. In addition, it is shown that with this experimental setup it is possible to measure atomic masses up to A=120 with accuracies of approximately 50 keV. [Copyright &y& Elsevier]

Abstract: Preliminary studies in preparation for an absolute cross-section measurement of the radiative capture reaction 3He()7Be with the DRAGON recoil separator have demonstrated beam suppression at the 90% confidence level. A measurement of this cross section by observation of 7Be recoils at the focal plane of the separator should be virtually background free. [Copyright &y& Elsevier]

The p -nuclei are the few stable nuclei heavier than iron on the neutron-deficient side of the valley of stability that cannot be produced through astrophysical neutron-capture reactions. The limited experimental data on reactions through which the p -nuclei might be produced leaves the origin of their production largely unknown. This work presents the first cross section measurements of the 76Se(α , γ)80Kr reaction. The rate of the time reversed reaction, 80Kr(γ , α)76Se, is one of the most uncertain of possible reactions which can occur at the 80Kr branching point on the γ -process photo-disintegration pathway. The reaction flow through 80Kr will directly affect the final abundance of the p -nuclide 78Kr. Experimental cross sections at two astrophysically relevant energies are reported and compared to cross sections calculated using Hauser-Feshbach codes talys , non-smoker , and smaragd. The success of these first (α , γ) cross section measurements performed in inverse kinematics in the energy region of the γ -process opens the door for future studies of reactions on radioactive γ -process nuclides. [ABSTRACT FROM AUTHOR]

In this Letter we report on the first inverse kinematics measurement of key resonances in the Ne 22 (p , γ) 23 Na reaction which forms part of the NeNa cycle, and is relevant for 23Na synthesis in asymptotic giant branch (AGB) stars. An anti-correlation in O and Na abundances is seen across all well-studied globular clusters (GC), however, reaction-rate uncertainties limit the precision as to which stellar evolution models can reproduce the observed isotopic abundance patterns. Given the importance of GC observations in testing stellar evolution models and their dependence on NeNa reaction rates, it is critical that the nuclear physics uncertainties on the origin of 23Na be addressed. We present results of direct strengths measurements of four key resonances in Ne 22 (p , γ) 23 Na at E c. m. = 149 keV, 181 keV, 248 keV and 458 keV. The strength of the important E c. m. = 458 keV reference resonance has been determined independently of other resonance strengths for the first time with an associated strength of ωγ = 0.439(22) eV and with higher precision than previously reported. Our result deviates from the two most recently published results obtained from normal kinematics measurements performed by the LENA and LUNA collaborations but is in agreement with earlier measurements. The impact of our rate on the Na-pocket formation in AGB stars and its relation to the O-Na anti-correlation was assessed via network calculations. Further, the effect on isotopic abundances in CO and ONe novae ejecta with respect to pre-solar grains was investigated. [ABSTRACT FROM AUTHOR]

During the slow neutron capture process in massive stars, reactions on light elements can both produce and absorb neutrons thereby influencing the final heavy element abundances. At low metallicities, the high neutron capture rate of 16O can inhibit s-process nucleosynthesis unless the neutrons are recycled via the 17O(α , n)20Ne reaction. The efficiency of this neutron recycling is determined by competition between the 17O(α , n)20Ne and 17O(α , γ)21Ne reactions. While some experimental data are available on the former reaction, no data exist for the radiative capture channel at the relevant astrophysical energies. The 17O(α , γ)21Ne reaction has been studied directly using the DRAGON recoil separator at the TRIUMF Laboratory. The reaction cross section has been determined at energies between 0.6 and 1.6 MeV E c m , reaching into the Gamow window for core helium burning for the first time. Resonance strengths for resonances at 0.63, 0.721, 0.81 and 1.122 MeV E c m have been extracted. The experimentally based reaction rate calculated represents a lower limit, but suggests that significant s-process nucleosynthesis occurs in low metallicity massive stars. [ABSTRACT FROM AUTHOR]

Background: Nucleosynthesis of mid-mass elements is thought to occur under hot and explosive astrophysical conditions. Radiative α capture on 34S has been shown to impact nucleosynthesis in several such conditions, including core and shell oxygen burning, explosive oxygen burning, and type Ia supernovae. Purpose: Broad uncertainties exist in the literature for the strengths of three resonances within the astrophysically relevant energy range (ECM=1.94-3.42MeV at T=2.2GK). Further, there are several states in 38Ar within this energy range which have not been previously measured. This work aimed to remeasure the resonance strengths of states for which broad uncertainty existed as well as to measure the resonance strengths and energies of previously unmeasured states. Methods: Resonance strengths and energies of eight narrow resonances (five of which had not been previously studied) were measured in inverse kinematics with the DRAGON facility at TRIUMF by impinging an isotopically pure beam of 34S ions on a windowless 4He gas target. Prompt γ emissions of de-exciting 38Ar recoils were detected in an array of bismuth germanate scintillators in coincidence with recoil nuclei, which were separated from unreacted beam ions by an electromagnetic mass separator and detected by a time-of-flight system and a multianode ionization chamber. Results: The present measurements agree with previous results. Broad uncertainty in the resonance strength of the ECM=2709keV resonance persists. Resonance strengths and energies were determined for five low-energy resonances which had not been studied previously, and their strengths were determined to be significantly weaker than those of previously measured resonances. Conclusions: The five previously unmeasured resonances were found not to contribute significantly to the total thermonuclear reaction rate. A median total thermonuclear reaction rate calculated using data from the present work along with existing literature values using the STARLIB rate calculator agrees with the NON-SMOKER statistical model calculation as well as the REACLIB and STARLIB library rates at explosive and nonexplosive oxygen-burning temperatures (T=3-4GK and T=1.5-2.7GK, respectively). [ABSTRACT FROM AUTHOR]

Background: Classical novae are cataclysmic nuclear explosions occurring when a white dwarf in a binary system accretes hydrogen-rich material from its companion star. Novae are partially responsible for the galactic synthesis of a variety of nuclides up to the calcium (A∼40) region of the nuclear chart. Although the structure and dynamics of novae are thought to be relatively well understood, the predicted abundances of elements near the nucleosynthesis endpoint, in particular Ar and Ca, appear to sometimes be in disagreement with astronomical observations of the spectra of nova ejecta. Purpose: One possible source of the discrepancies between model predictions and astronomical observations is nuclear reaction data. Most reaction rates near the nova endpoint are estimated only from statistical model calculations, which carry large uncertainties. For certain key reactions, these rate uncertainties translate into large uncertainties in nucleosynthesis predictions. In particular, the 38K(p,γ)39Ca reaction has been identified as having a significant influence on Ar, K, and Ca production. In order to constrain the rate of this reaction, we have performed a direct measurement of the strengths of three candidate ℓ=0 resonances within the Gamow window for nova burning, at 386±10 keV, 515±10 keV, and 689±10 keV. Method: The experiment was performed in inverse kinematics using a beam of unstable 38K impinged on a windowless hydrogen gas target. The 39Ca recoils and prompt γ rays from 38K(p,γ)39Ca reactions were detected in coincidence using a recoil mass separator and a bismuth-germanate scintillator array, respectively. Results: For the 689 keV resonance, we observed a clear recoil-γ coincidence signal and extracted resonance strength and energy values of 120-30+50(stat.)-60+20(sys.)meV and 679+2-1(stat.)±1(sys.)keV, respectively. We also performed a singles analysis of the recoil data alone, extracting a resonance strength of 120±20(stat.)±15(sys.) meV, consistent with the coincidence result. For the 386 keV and 515 keV resonances, we extract 90% confidence level upper limits of 2.54 meV and 18.4 meV, respectively. Conclusions: We have established a new recommended 38K(p,γ)39Ca rate based on experimental information, which reduces overall uncertainties near the peak temperatures of nova burning by a factor of ∼250. Using the rate obtained in this work in model calculations of the hottest oxygen-neon novae reduces overall uncertainties on Ar, K, and Ca synthesis to factors of 15 or less in all cases. [ABSTRACT FROM AUTHOR]

Background: The rate of the 18F(p,γ)19Ne reaction affects the final abundance of the radioisotope 18F ejected from novae. This nucleus is important as its abundance is thought to significantly influence the first-stage 511-keV and continuum γ-ray emission in the aftermath of novae. No successful measurement of this reaction existed prior to this work, and the rate used in stellar models had been calculated based on incomplete information from contributing resonances. Purpose: Of the two resonances thought to provide a significant contribution to the astrophysical reaction rate, located at Ec.m.=330 and 665 keV, the former has a radiative width estimated from the assumed analog state in the mirror nucleus, 19F, while the latter resonance does not have an analog state assignment, resulting in an arbitrary radiative width being assumed. As such, a direct measurement was needed to establish what role this resonance plays in the destruction of 18F at nova temperatures. This paper extends and takes the place of a previous Letter which reported the strength of the Ec.m.=665 keV resonance. Method: The DRAGON recoil separator was used to directly measure the strength of the important 665-keV resonance in this reaction, in inverse kinematics, by observing 19Ne reaction products. A radioactive 18F beam was provided by the ISAC facility at TRIUMF. R-matrix calculations were subsequently used to evaluate the significance of the results at astrophysical energies. Results: We report the direct measurement of the 18F(p,γ)19Ne reaction with the reevaluation of several detector efficiencies and the use of an updated 19Ne level scheme in the reaction rate analysis. The strength of the 665-keV resonance (Ex=7.076 MeV) is found to be an order of magnitude weaker than currently assumed in nova models. An improved analysis of the previously reported data is presented here, resulting in a slightly different value for the resonance strength. These small changes, however, do not alter the primary conclusions. Conclusions: Reaction rate calculations definitively show that the 665-keV resonance plays no significant role in the destruction of 18F at nova temperatures. [ABSTRACT FROM AUTHOR]

We have performed the first direct measurement of the 38K(p,γ)39Ca reaction using a beam of radioactive 38K. A proposed ℓ=0 resonance in the 38K+p system has been identified at 679(2) keV with an associated strength of 120+50−30  meV. Upper limits of 1.16 (3.5) and 8.6 (26) meV at the 68% (95%) confidence level were also established for two further expected ℓ=0 resonances at 386 and 515 keV, respectively. The present results have reduced uncertainties in the 38K(p,γ)39Ca reaction rate at temperatures of 0.4 GK by more than 2 orders of magnitude and indicate that Ar and Ca may be ejected in observable quantities by oxygen-neon novae. However, based on the newly evaluated rate, the 38K(p,γ)39Ca path is unlikely to be responsible for the production of Ar and Ca in significantly enhanced quantities relative to solar abundances. [ABSTRACT FROM AUTHOR]

A series of beta decay experiments on nuclei near the Z = N line has been performed using the ISOL technique at the IGISOL facility in Jyväskylä and at ISOLDE, CERN. The decay properties of these neutron-deficient nuclei are important in astrophysics as well as in the studies of isospin symmetry. [ABSTRACT FROM AUTHOR]

Angular distributions of the elastic, inelastic, and breakup cross sections of the halo nucleus ^{11}Be on ^{197}Au were measured at energies below (E_{lab}=31.9  MeV) and around (39.6 MeV) the Coulomb barrier. These three channels were unambiguously separated for the first time for reactions of ^{11}Be on a high-Z target at low energies. The experiment was performed at TRIUMF (Vancouver, Canada). The differential cross sections were compared with three different calculations: semiclassical, inert-core continuum-coupled-channels and continuum-coupled-channels ones with including core deformation. These results show conclusively that the elastic and inelastic differential cross sections can only be accounted for if core-excited admixtures are taken into account. The cross sections for these channels strongly depend on the B(E1) distribution in ^{11}Be, and the reaction mechanism is sensitive to the entanglement of core and halo degrees of freedom in ^{11}Be.

We have performed the first direct measurement of the ^{38}K(p,γ)^{39}Ca reaction using a beam of radioactive ^{38}K. A proposed ℓ=0 resonance in the ^{38}K+p system has been identified at 679(2) keV with an associated strength of 120_{-30}^{+50}  meV. Upper limits of 1.16 (3.5) and 8.6 (26) meV at the 68% (95%) confidence level were also established for two further expected ℓ=0 resonances at 386 and 515 keV, respectively. The present results have reduced uncertainties in the ^{38}K(p,γ)^{39}Ca reaction rate at temperatures of 0.4 GK by more than 2 orders of magnitude and indicate that Ar and Ca may be ejected in observable quantities by oxygen-neon novae. However, based on the newly evaluated rate, the ^{38}K(p,γ)^{39}Ca path is unlikely to be responsible for the production of Ar and Ca in significantly enhanced quantities relative to solar abundances.

Topically applied camphor elicits a sensation of cool, but nothing is known about how it affects cold temperature sensing. We found that camphor sensitizes a subpopulation of menthol-sensitive native cutaneous nociceptors in the mouse to cold, but desensitizes and partially blocks heterologously expressed TRPM8 (transient receptor potential cation channel subfamily M member 8). In contrast, camphor reduces potassium outward currents in cultured sensory neurons and, in cold nociceptors, the cold-sensitizing effects of camphor and menthol are additive. Using a membrane potential dye-based screening assay and heterologously expressed potassium channels, we found that the effects of camphor are mediated by inhibition of Kv7.2/3 channels subtypes that generate the M-current in neurons. In line with this finding, the specific M-current blocker XE991 reproduced the cold-sensitizing effect of camphor in nociceptors. However, the M-channel blocking effects of XE991 and camphor are not sufficient to initiate cold transduction but require a cold-activated inward current generated by TRPM8. The cold-sensitizing effects of XE991 and camphor are largest in high-threshold cold nociceptors. Low-threshold corneal cold thermoreceptors that express high levels of TRPM8 and lack potassium channels are not affected by camphor. We also found that menthol--like camphor--potently inhibits Kv7.2/3 channels. The apparent functional synergism arising from TRPM8 activation and M-current block can improve the effectiveness of topical coolants and cooling lotions, and may also enhance TRPM8-mediated analgesia.

The rate of the 18F(p,γ)19Ne reaction affects the final abundance of the γ-ray observable radioisotope 18F, produced in novae. However, no successful measurement of this reaction exists and the rate used is calculated from incomplete information on the contributing resonances. Of the two resonances thought to play a significant role, one has a radiative width estimated from the assumed analogue state in the mirror nucleus, 19F. The second does not have an analogue state assignment at all, resulting in an arbitrary radiative width being assumed. Here, we report the first successful direct measurement of the 18F(p,γ)^19Ne reaction. The strength of the 665 keV resonance (Ex=7.076  MeV) is found to be over an order of magnitude weaker than currently assumed in nova models. Reaction rate calculations show that this resonance therefore plays no significant role in the destruction of ^{18}F at any astrophysical energy.

The β feeding probability of (102,104,105,106,107)Tc, 105Mo, and 101Nb nuclei, which are important contributors to the decay heat in nuclear reactors, has been measured using the total absorption technique. We have coupled for the first time a total absorption spectrometer to a Penning trap in order to obtain sources of very high isobaric purity. Our results solve a significant part of a long-standing discrepancy in the γ component of the decay heat for 239Pu in the 4-3000 s range.

This protocol details methods to identify and record from cutaneous primary afferent axons in an isolated mammalian skin-saphenous nerve preparation. The method is based on extracellular recordings of propagated action potentials from single-fiber receptive fields. Cutaneous nerve endings show graded sensitivities to various stimulus modalities that are quantified by adequate and controlled stimulation of the superfused skin with heat, cold, touch, constant punctate pressure or chemicals. Responses recorded from single-fibers are comparable with those obtained in previous in vivo experiments on the same species. We describe the components and the setting-up of the basic equipment of a skin-nerve recording station (few days), the preparation of the skin and the adherent saphenous nerve in the mouse (15-45 min) and the isolation and recording of neurons (approximately 1-3 h per recording). In addition, stimulation techniques, protocols to achieve single-fiber recordings, issues of data acquisition and action potential discrimination are discussed in detail.

High-precision mass measurements on neutron-rich zinc isotopes (71m,72-81)Zn have been performed with the Penning trap mass spectrometer ISOLTRAP. For the first time, the mass of 81Zn has been experimentally determined. This makes 80Zn the first of the few major waiting points along the path of the astrophysical rapid neutron-capture process where neutron-separation energy and neutron-capture Q-value are determined experimentally. The astrophysical conditions required for this waiting point and its associated abundance signatures to occur in r-process models can now be mapped precisely. The measurements also confirm the robustness of the N=50 shell closure for Z=30.

Atomic masses of the neutron-rich isotopes (76-80)Zn, (78-83)Ga, (80-85)Ge, (81-87)As, and (84-89)Se have been measured with high precision using the Penning trap mass spectrometer JYFLTRAP at the IGISOL facility. The masses of (82,83)Ga, (83-85)Ge, (84-87)As, and 89Se were measured for the first time. These new data represent a major improvement in the knowledge of the masses in this neutron-rich region. Two-neutron separation energies provide evidence for the reduction of the N=50 shell gap energy towards germanium (Z=32) and a subsequent increase at gallium (Z=31). The data are compared with a number of theoretical models. An indication of the persistent rigidity of the shell gap towards nickel (Z=28) is obtained.

Using a new fast cleaning procedure to prepare isomerically pure ion samples, we have measured the beta-decay Q(EC) values of the superallowed beta emitters 5(0)Mn and (54)Co to be 7634.48(7) and 8244.54(10) keV, respectively, results which differ significantly from the previously accepted values. The corrected Ft values derived from our results strongly support new isospin-symmetry-breaking corrections that lead to a higher value of the up-down quark mixing element V(ud) and improved confirmation of the unitarity of the Cabibbo-Kobayashi-Maskawa matrix.

A high-precision direct Penning trap mass measurement has revealed a 0.5-MeV deviation of the binding energy of (134)Sn from the currently accepted value. The corrected mass assignment of this neutron-rich nuclide restores the neutron-shell gap at N=82, previously considered to be a case of "shell quenching." In fact, the new shell gap value for the short-lived (132)Sn is larger than that of the doubly magic (48)Ca which is stable. The N=82 shell gap has considerable impact on fission recycling during the r process. More generally, the new finding has important consequences for microscopic mean-field theories which systematically deviate from the measured binding energies of closed-shell nuclides.

A recently described family of "orphan" receptors, called Mas-related G-protein-coupled receptors (Mrg), is preferentially expressed in small nociceptive neurons of the rodent and human dorsal root ganglia (DRG). Mrg are activated by high affinity peptide fragments derived from the proenkephalin A gene, e.g. BAM22 (bovine adrenal medullary). To study the histological distribution and functional properties of these receptors, we combined confocal immunohistochemistry in rat DRG and dermis whole mounts, using new antibodies against the rat Mas-related G-protein-coupled receptor C (MrgC), with single-fiber recordings and neurochemical experiments using isolated hind-paw skin and sciatic nerve. In lumbar DRG we found cytoplasmic MrgC labeling mainly in small- and medium-sized neurons; coexpression with isolectin B4 (46%) and transient receptor potential vanilloid receptor 1 channel protein (TRPV1) (52%) occurred frequently, whereas calcitonin gene-related peptide (CGRP) was rarely colocalized with MrgC in DRG (11%) and dermal nerve fibers (6%). One of the MrgC agonists, BAM22, more than doubled the heat-induced cutaneous CGRP release from rat and mouse skin. The effect of BAM22, also known to activate opioid receptors, was further enhanced by combination with naloxone that had no effect on its own. This sensitizing effect proved to be independent of secondary prostaglandin formation, mast cell degranulation, protein kinase C (PKC) activation and independent of TRPV1. Nonetheless, the capsaicin-induced CGRP release was also sensitized. Receptive fields of 26 mechano-heat sensitive C-fibers were treated with MrgC agonists. Only one unit was strongly and repeatedly excited and showed a profound sensitization to heat upon BAM22+naloxone. Two other established MrgC agonists (gamma2-melanocyte stimulating hormone and BAM8-22) were ineffective. Thus, BAM22 sensitizes the capsaicin- and heat-induced CGRP release in an apparently MrgC-unrelated way. The sensitization to heat appears unusually resistant against pharmacological interventions and does not involve TRPV1.

The beta-decay Q(EC) values of the superallowed beta emitters 26Alm, 42Sc, and 46V have been measured with a Penning trap to a relative precision of better than 8 x 10(-9). Our result for 46V, 7052.72(31) keV, confirms a recent measurement that differed from the previously accepted reaction-based Q(EC) value. However, our results for 26Alm and 42Sc, 4232.83(13) keV and 6426.13(21) keV, are consistent with previous reaction-based values. By eliminating the possibility of a systematic difference between the two techniques, this result demonstrates that no significant shift in the deduced value of Vud should be anticipated.

Objective: To investigate the effectiveness of a clinical treatment program with traditional Chinese medicine for migraine and tension-type headache., Methods: Ninety-one patients with migraine, episodic or chronic tension-type headache according to the criteria of the International Headache Society were randomised into an experimental or a waiting list control group. Patients in the experimental group were treated 4 weeks in a hospital for traditional Chinese medicine after a baseline period of one month. Patients in the waiting list group continued their previous headache treatment. Main outcome measure was the difference in the number of days with headache of at least moderate intensity during baseline (month 1) and month 7., Results: The difference in the number of days with headache of at least moderate intensity was 5.6 (S.D., 6.1) days in the experimental group and 1.2 (S.D., 4.5) days in the waiting list group (P <0.001). A reduction of more than 50% in headache days was observed in 52% of the patients in the experimental group and 16% in the waiting list group. Patients with migraine and a combination of migraine and episodic tension-type headaches improved more than patients with other headaches., Conclusion: The results of this study indicate that treatment in the hospital for traditional Chinese medicine in Kotzting is associated with lasting improvements in the majority of patients.

There is still not sufficient in-depth knowledge available concerning the type and extent of the interdependencies between the large number of factors that influence, on the one hand, urban and transport planning, and on the other hand, road safety. If such in-depth knowledge did, in fact, exist this information would make it possible to recommend courses of action to urban planning authorities. The present study aims to remove this data deficit so that planning authorities may be able to assess not only the effects expected from individual measures but also to evaluate, with respect to the level of road safety, an entire planning area. The empirical study is based on 21 typical residential areas for which a total of 56 characteristics (variables) relating to the following sectors have been identified as descriptors of the accident situation: transport; local development structure; infrastructure facilities other than those intended for transport; and population structure. The statistical analysis was undertaken in two steps: correlation analysis of all variables; identification of the determinants of significance for road safety; and establishment of a non-linear regression model based on seven variables to express the relationship between transport provisions and traffic volumes as well as the quality of supply and demand in quantitative terms. By means of the regression model the accident load can, in principle, be assessed for any given residential area. The correlation analysis showed that there are still further influential factors which are of importance for road safety. Attempts were therefore made to identify the variables displaying a significant relationship to the model variables and which could thus, owing to their effects on the latter and the resulting linkage with road safety, be considered as "background variables." Whereas the majority of the model variables are to be ascribed to the transport sector, the so-called "background variables" mainly relate to other areas of urban development. Based on the elasticities of the variables describing various levels of dependencies, an evaluation procedure has been developed. Based on this the applicability of the research findings to urban planning operations can be assessed. The contributions to road safety of the different variables can be quantified and compared, and recommended courses of action can be derived from this procedure.(ABSTRACT TRUNCATED AT 400 WORDS)