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  • 11
    Electronic Resource
    Electronic Resource
    Fluctuations in absorption spectra and final product state distributions following photodissociation processes (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 2051-2068 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a quantum mechanical wave packet study for the unimolecular dissociation of a triatomic molecule into an atom and a diatom. The 3D potential energy surface used in the dynamics calculations is that of the B˜ state of water corresponding to the second absorption band. Both OH stretching coordinates and the bending angle are included. What is not taken into account is the strong nonadiabatic coupling to the lower-lying A˜ and X˜ states which in reality drastically shortens the lifetime in the B˜ state. For this reason the present study is not a realistic account of the dissociation dynamics of water in the 122 nm band. It is, however, a representational investigation of a unimolecular reaction evolving on a realistic potential energy surface without barrier. The main focus is the resonance structure of the absorption spectrum and the final rotational state distributions of the OH fragment. The total absorption spectrum as well as the partial dissociation cross sections for individual rotational states of OH show drastic fluctuations caused by overlapping resonances. The widths of the individual resonances increase, on average, with the excess energy which has the consequence that the cross sections become gradually smoother. Although the low-energy part of the spectrum is rather irregular, it shows "clumps'' of resonances with an uniform spacing of ∼0.1 eV. They are discussed in the context of IVR and a particular unstable periodic orbit. In accordance with the fluctuations in the partial dissociation cross sections as functions of the excess energy the final rotational state distributions show pronounced, randomlike fluctuations which are extremely sensitive on the energy.The average is given by the statistical limit (PST), in which all levels are populated with equal probability. With increasing excess energy the distributions more and more exhibit dynamical features which are reminiscent of direct dissociation like rainbows and associated interferences. Classical trajectories for small excess energies are chaotic, as tested by means of the rotational excitation function, but become gradually more regular with increasing energy. Our wave packet calculations hence demonstrate how the transition from the chaotic to the regular regime shows up in a fully quantum mechanical treatment. The results of the present investigation are in qualitative accord with recent measurements for the unimolecular dissociation of NO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467713
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  • 12
    Electronic Resource
    Electronic Resource
    Photodissociation of HF in ArnHF (n=1–14,54) van der Waals clusters: Effects of the solvent cluster size on the solute fragmentation dynamics (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 9228-9241 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A comprehensive study of the photodissociation of HF in ArnHF van der Waals clusters, with n=1−14,54, for an ultrashort δ(t)-pulse excitation, is presented. The emphasis is on the dependence of the photodissociation dynamics of the HF solute molecule on the size and geometry of the Arn solvent cluster. This cluster size range encompasses formation and closing of the first solvation shell, which occurs for n=12, the addition of the complete second solvent layer (n=54), as well as the change of the HF location in the cluster, from a surface site for n≤8 to the interior of a cage for n≥9 clusters. Evolution of the fragmentation dynamics is revealed by following how the H-atom kinetic energy and angular distributions, the survival probability, and cluster fragmentation patterns change as a function of the cluster size and structure. Classical trajectories are used to simulate the photodissociation dynamics. The probability distributions of the initial coordinates and momenta of the H and F atom are defined by accurate quantum five-dimensional eigenstates of the coupled, very anharmonic large amplitude intermolecular vibrations of HF in the cluster. All aspects of the dissociation process studied here are found to exhibit a strong dependence on the size and geometry of the ArnHF clusters. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470034
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  • 13
    Electronic Resource
    Electronic Resource
    Square-wave, polarographic determination of lead as a pollutant in river water (1970)
    s.l. : American Chemical Society
    Analytical chemistry 42 (1970), S. 370-373 
    Details
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ac60285a001
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  • 14
    Electronic Resource
    Electronic Resource
    New aspects of the photodissociation of water in the first absorption band: How strong is excitation of the first triplet state? (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 6641-6646 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We consider the possibility of the X˜ 1A1→3B1 excitation of water at wavelengths near 193 nm, i.e., in the red tail of the first absorption band. The corresponding excited-state potential-energy surface is calculated by quantum mechanical methods and the dynamics calculations are performed in the time-dependent representation. It is shown that an absorption cross section for exciting the triplet state 3B1, that at its maximum is about five hundred times (or more) smaller than the corresponding cross section for excitation of the 1B1 state, might explain the surprisingly small H+OD/D+OH branching ratio in the photodissociation of HOD at 193 nm measured by Plusquellic et al. (the foregoing paper). The singlet–triplet transition dipole moment estimated in this way also explains the unexpectedly small cross section ratio for H2O and D2O measured at 193 nm. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477315
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  • 15
    Electronic Resource
    Electronic Resource
    Unimolecular dissociation dynamics of highly vibrationally excited DCO(X˜ 2A). II. Calculation of resonance energies and widths and comparison with high-resolution spectroscopic data (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 5359-5378 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a theoretical study of the unimolecular dissociation of DCO in the electronic ground state, X˜ 1A, using a new ab initio potential energy surface. Altogether we have analyzed about 140 resonances up to an energy of (approximate)1.4 eV above the D+CO threshold, corresponding to the ninth overtone in the CO stretching mode (v2=9). The agreement of the resonance positions and widths with recent stimulated emission pumping measurements of Stöck et al. [J. Chem. Phys. 106, 5333 (1997), the preceding article] is pleasing. The root-mean-square deviation from the experimental energies is only 16 cm−1 over a range of about 16 500 cm−1 and all trends of the resonance widths observed in the experiment are satisfactorily reproduced by the calculations. A strong 1:1:2 stretch–stretch–bend resonance prohibits a unique assignment for the majority of vibrational states. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473599
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  • 16
    Electronic Resource
    Electronic Resource
    Paradoxical puborectalis contraction in children (1992)
    Springer
    Diseases of the colon & rectum 35 (1992), S. 1193-1194 
    Details
    ISSN: 1530-0358
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02251977
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  • 17
    Electronic Resource
    Electronic Resource
    Endoluminal ultrasound is preferable to electromyography in mapping anal sphincteric defects (1993)
    Springer
    Diseases of the colon & rectum 36 (1993), S. 689-692 
    Details
    ISSN: 1530-0358
    Keywords: Ultrasound ; Imaging ; Electromyography ; Anus ; Anal sphincters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Assessment of complex sphincteric defects in patients with fecal incontinence by digital rectal examination and intraoperative dissection can be difficult in the presence of excessive scarring. Adjunctive investigation such as endoluminal ultrasound (ELUS) and needle electromyography (EMG) may provide objective evidence of the nature and extent of the sphincteric defects. In a series of 11 patients, ELUS of the anal canal with a 10-MHz transducer (focal zone of 1–4 cm) accurately detected defects in the external anal sphincter (EAS) in seven of seven patients, defects in the internal anal sphincter (IAS) in eight of eight patients, and integrity of both sphincters in two patients. These findings were confirmed by needle EMG of the EAS alone in five patients, by operative findings at a perineal sphincteroplasty operation in six patients, and by both in two patients. ELUS was associated with less pain than was needle EMG (pain score 4vs. 10, 10 being most painful) and provided high-resolution radial images of both the EAS and the IAS. Thus, ELUS seems preferable to EMG in mapping anal sphincteric defects and can be a useful anatomic adjunct to physiologic studies of anorectal function in patients with fecal incontinence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02238597
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  • 18
    Electronic Resource
    Electronic Resource
    Safety of urgent restorative proctocolectomy with ileal pouch-anal anastomosis for fulminant colitis (1995)
    Springer
    Diseases of the colon & rectum 38 (1995), S. 345-349 
    Details
    ISSN: 1530-0358
    Keywords: Fulminant colitis ; Ileal pouch-anal anastomosis ; Surgery
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract PURPOSE: Subtotal colectomy with ileostomy is the operation of choice for patients with fulminant colitis. Restorative proctocolectomy (RPC) with ileal pouch-anal anastomosis (IPAA) is preferred for patients who undergo elective surgery for ulcerative colitis. We retrospectively evaluated the safety of RPC with IPAA in patients with a moderate form of fulminant colitis. METHODS: A chart review of 737 patients who underwent RPC with IPAA for ulcerative and indeterminate colitis from 1983 through 1992 was performed. Moderate fulminant colitis was defined as acute disease requiring hospitalization and parenteral steroid therapy, but without hypotension (systolic blood pressure, 〈100 mmHg), tachycardia (〉120 beats/min), or megacolon. RESULTS: Twelve patients with moderate fulminant colitis underwent urgent surgery (1.6 percent). They had been treated preoperatively for 5.1±2.3 days with intravenous high-dose steroids, total parenteral nutrition, and antibiotics. These patients had a shorter length of disease ( P =0.01), lower hemoglobin, hematocrit, and albumin (P=0.001), and higher temperature (P=0.002) and leukocyte count (P=0.007) than patients undergoing elective surgery. No early septic complications occurred, although perianal abscess occurred in one patient and pouch-anal fistula in another patient, 13 and 14 months after surgery, respectively. CONCLUSION: In carefully selected, hemodynamically stable patients with fulminant colitis and without megacolon, RPC with IPAA can be safely performed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02054219
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  • 19
    Electronic Resource
    Electronic Resource
    The toxicity of four insecticides to four salmonid species (1971)
    Springer
    Bulletin of environmental contamination and toxicology 6 (1971), S. 144-155 
    Details
    ISSN: 1432-0800
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01540097
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  • 20
    Electronic Resource
    Electronic Resource
    The contractile ring (1970)
    Springer
    Cell & tissue research 109 (1970), S. 431-449 
    Details
    ISSN: 1432-0878
    Keywords: Contractile ring ; Cytokinesis ; Cell division ; Cytochalasin B ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Techniques of individual cell selection and precise ultramicrotomy have been employed to demonstrate that the contractile ring of cleaving HeLa cells is a transitory cytoplasmic organelle of distinctive fine structure and location. The contractile ring is an uninterrupted annulus encircling the equator of dividing cells exactly where the cleavage furrow forms. It is about 10 microns wide, up to 0.2 microns in thickness, and is composed exclusively of circumferentially aligned thin filaments 40–70 Å in diameter. Contractile ring filaments appear to be associated with the overlying plasma membrane. Controlled experiments with a mold metabolite (cytochalasin B) reveals that within a few minutes the drug abolishes the ability of HeLa cells to undergo cytokinesis. Cytochalasin B seems to decompose the contractile ring. It has no other clearly identifiable effects on other cell structures, notably the mitotic apparatus. Cytochalasin B is the only drug known which selectively inhibits cytokinesis in animal cells. In conclusion, the contractile ring is the most likely organelle responsible for cytokinesis in HeLa cells. Similar organelles probably occur in all cleaving animal cells. Successful cleavage depends upon the structural and functional integrity of the contractile ring.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00343960
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