Quantum manifestations of scattering orbits in the scaled spectrum of a non-hydrogenic atom in crossed fields

Evidence for scattering closed orbits for the Rydberg electron of the singly excited helium atom in crossed electric and magnetic fields at constant scaled energy and constant scaled electric field strength has been found through a quantum calculation of the photo-excitation spectrum. A particular 3D scattering orbit in a mixed regular and chaotic region has been investigated and the hydrogenic 3D closed orbits composing it identified. To the best of our knowledge, this letter reports the first quantum calculation of the scaled spectrum of a non- hydrogenic atom in crossed fields.

Quantum manifestations of closed orbits in the photoexcitation scaled spectrum of the hydrogen atom in crossed fields

The scaled photoexcitation spectrum of the hydrogen atom in crossed electric and magnetic fields has been obtained by means of accurate quantum mechanical calculation using a new algorithm. Closed orbits in the corresponding classical system have also been obtained, using a new, efficient and practical searching procedure. Two new classes of closed orbit have been identified. Fourier transforming each photoexcitation quantum spectrum to yield a plot against scaled action has allowed direct comparison between peaks in such plots and the scaled action values of closed orbits, Excellent agreement has been found with all peaks assigned.

The closed orbits and the photo-excitation scaled spectrum of the hydrogen atom in crossed fields

In a recent Letter to the Editor (J Rao, D Delande and K T Taylor 2001 J. Phys. B: At. Mol. Opt. Phys. 34 L391-9) we made a brief first report of our quantal and classical calculations for the hydrogen atom in crossed electric and magnetic fields at constant scaled energy and constant scaled electric field strength. A principal point of that communication was our statement that each and every peak in the Fourier transform of the scaled quantum photo-excitation spectrum for scaled energy value epsilon = -0.586 538 871028 43 and scaled electric value (f) over tilde = 0.068 537 846 207 618 71 could be identified with a scaled action value of a found and mapped-out closed orbit up to a scaled action of 20. In this follow-up paper, besides presenting full details of our quantum and classical methods, we set out the scaled action values of all 317 closed orbits involved, together with the geometries of many.

Ion-Atom/Argon - Calculation of ionization cross sections by fast ion impact for neutral target atoms ranging from hydrogen to argon

A FORTRAN 90 program is presented which calculates the total cross sections, and the electron energy spectra of the singly and doubly differential cross sections for the single target ionization of neutral atoms ranging from hydrogen up to and including argon. The code is applicable for the case of both high and low Z projectile impact in fast ion-atom collisions. The theoretical models provided for the program user are based on two quantum mechanical approximations which have proved to be very successful in the study of ionization in ion-atom collisions. These are the continuum-distorted-wave (CDW) and continuum-distorted-wave eikonal-initial-state (CDW-EIS) approximations. The codes presented here extend previously published. codes for single ionization of. target hydrogen [Crothers and McCartney, Comput. Phys. Commun. 72 (1992) 288], target helium [Nesbitt, O'Rourke and Crothers, Comput. Phys. Commun. 114 (1998) 385] and target atoms ranging from lithium to neon [O'Rourke, McSherry and Crothers, Comput. Phys. Commun. 131 (2000) 129]. Cross sections for all of these target atoms may be obtained as limiting cases from the present code. Title of program: ARGON Catalogue identifier: ADSE Program summary URL: http://cpc.cs.qub.ac.uk/cpc/summaries/ADSE Program obtainable from: CPC Program Library Queen's University of Belfast, N. Ireland Licensing provisions: none Computer for which the program is designed and others on which it is operable: Computers: Four by 200 MHz Pro Pentium Linux server, DEC Alpha 21164; Four by 400 MHz Pentium 2 Xeon 450 Linux server, IBM SP2 and SUN Enterprise 3500 Installations: Queen's University, Belfast Operating systems under which the program has been tested: Red-hat Linux 5.2, Digital UNIX Version 4.0d, AIX, Solaris SunOS 5.7 Compilers: PGI workstations, DEC CAMPUS Programming language used: FORTRAN 90 with MPI directives No. of bits in a word: 64, except on Linux servers 32 Number of processors used: any number Has the code been vectorized or parallelized? Parallelized using MPI No. of bytes in distributed program, including test data, etc.: 32 189 Distribution format: tar gzip file Keywords: Single ionization, cross sections, continuum-distorted-wave model, continuum- distorted-wave eikonal-initial-state model, target atoms, wave treatment Nature of physical problem: The code calculates total, and differential cross sections for the single ionization of target atoms ranging from hydrogen up to and including argon by both light and heavy ion impact. Method of solution: ARGON allows the user to calculate the cross sections using either the CDW or CDW-EIS [J. Phys. B 16 (1983) 3229] models within the wave treatment. Restrictions on the complexity of the program: Both the CDW and CDW-EIS models are two-state perturbative approximations. Typical running time: Times vary according to input data and number of processors. For one processor the test input data for double differential cross sections (40 points) took less than one second, whereas the test input for total cross sections (20 points) took 32 minutes. Unusual features of the program: none (C) 2003 Elsevier B.V All rights reserved.

Surface alloying and mixing at the Mn/Fe(001) interface: Real-time photoelectron spectroscopy and modified embedded atom simulations

Structural and magnetic properties of thin Mn films on the Fe(001) surface have been investigated by a combination of photoelectron spectroscopy and computer simulation in the temperature range 300 Kless than or equal toTless than or equal to750 K. Room-temperature as deposited Mn overlayers are found to be ferromagnetic up to 2.5-monolayer (ML) coverage, with a magnetic moment parallel to that of the iron substrate. The Mn atomic moment decreases with increasing coverage, and thicker samples (4-ML and 4.5-ML coverage) are antiferromagnetic. Photoemission measurements performed while the system temperature is rising at constant rate (dT/dtsimilar to0.5 K/s) detect the first signs of Mn-Fe interdiffusion at T=450 K, and reveal a broad temperature range (610 Kless than or equal toTless than or equal to680 K) in which the interface appears to be stable. Interdiffusion resumes at Tgreater than or equal to680 K. Molecular dynamics and Monte Carlo simulations allow us to attribute the stability plateau at 610 Kless than or equal toTless than or equal to680 K to the formation of a single-layer MnFe surface alloy with a 2x2 unit cell and a checkerboard distribution of Mn and Fe atoms. X-ray-absorption spectroscopy and analysis of the dichroic signal show that the alloy has a ferromagnetic spin structure, collinear with that of the substrate. The magnetic moments of Mn and Fe atoms in the alloy are estimated to be 0.8mu(B) and 1.1mu(B), respectively.

Kit-positive interstitial cells in the rabbit urethra: structural relationships with nerves and smooth muscle.

OBJECTIVE: To identify interstitial cells (ICs) in the wall of the rabbit urethra using antibodies to the Kit receptor, and to examine their location, morphology and relationship with nerves and smooth muscle cells (SMCs), as studies of enzymatically isolated cells from the rabbit urethra have established that there are specialized cells that show spontaneous electrical activity and have morphological properties of ICs. MATERIALS AND METHODS: Urethral tissues from rabbits were fixed, labelled with antibodies and examined with confocal microscopy. Some specimens were embedded in paraffin wax and processed for histology. Histological sections from the most proximal third and mid-third region of rabbit urethra were stained with Masson's Trichrome to show their cellular arrangement. RESULTS: Sections from both regions had outer longitudinal and inner circular layers of SM, and a lamina propria containing connective tissue and blood vessels; the lumen was lined with urothelial cells. The mid-third region had a more developed circular SM layer than the most-proximal samples, and had extensive inner longitudinal SM bundles in the lamina propria. Labelling with anti-Kit revealed immunopositive cells within the wall of the rabbit urethra, in the circular and longitudinal layers of the muscularis. Double-labelling with an antibody to SM myosin showed Kit-positive cells on the boundary of the SM bundles, orientated parallel to the axis of the bundles. Others were in spaces between the bundles and often made contact with each other. Kit-positive cells were either elongated, with several lateral branches, or stellate with branches coming from a central soma. Similar cells could be labelled with vimentin antibodies. Their relationship with intramural nerves was examined by double immunostaining with an anti-neurofilament antibody. There were frequent points of contact between Kit-positive cells and nerves, with similar findings in specimens double-immunostained with anti-neuronal nitric oxide synthase (nNOS). CONCLUSION: Kit-positive ICs were found within the SM layers of the rabbit urethra, in association with nerves, on the edge of SM bundles and in the interbundle spaces. The contact with nNOS-containing neurones might imply participation in the nitrergic inhibitory neurotransmission of the urethra. PMID: 17212607 [PubMed - indexed for MEDLINE]

Cholinergic-induced Ca2+ signaling in interstitial cells of Cajal from the guinea pig bladder.

Acetylcholine released from parasympathetic excitatory nerves activates contraction in detrusor smooth muscle. Immunohistochemical labeling of guinea pig detrusor with anti-c-Kit and anti-VAChT demonstrated a close structural relationship between interstitial cells of Cajal (ICC) and cholinergic nerves. The ability of guinea pig bladder detrusor ICC to respond to the acetylcholine analog, carbachol, was investigated in enzymatically dissociated cells, loaded with the Ca(2+) indicator fluo 4AM. ICC fired Ca(2+) transients in response to stimulation by carbachol (1/10 microM). Their pharmacology was consistent with carbachol-induced contractions in strips of detrusor which were inhibited by 4-DAMP (1 microM), an M(3) receptor antagonist, but not by the M(2) receptor antagonist methoctramine (1 microM). The source of Ca(2+) underlying the carbachol transients in isolated ICC was investigated using agents to interfere with influx or release from intracellular stores. Nifedipine (1 microM) or Ni(2+) (30-100 microM) to block Ca(2+) channels or the removal of external Ca(2+) reduced the amplitude of the carbachol transients. Application of ryanodine (30 microM) or tetracaine (100 microM) abolished the transients. The phospholipase C inhibitor, U-73122 (2.5 microM), significantly reduced the responses. 2-Aminoethoxydiethylborate (30 microM) caused a significant reduction and Xestospongin C (1 microM) was more effective, almost abolishing the responses. Intact in situ preparations of guinea pig bladder loaded with a Ca(2+) indicator showed distinctively different patterns of spontaneous Ca(2+) events in smooth muscle cells and ICC. Both cell types responded to carbachol by an increase in frequency of these events. In conclusion, guinea pig bladder detrusor ICC, both as isolated cells and within whole tissue preparations, respond to cholinergic stimulation by firing Ca(2+) transients. PMID: 18171995 [PubMed - indexed for MEDLINE]