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PubMed2005

A simplified relativistic time-dependent density-functional theory formalism for the calculations of excitation energies including spin-orbit coupling effect.

In the present work we have proposed an approximate time-dependent density-functional theory (TDDFT) formalism to deal with the influence of spin-orbit coupling effect on the excitation energies for closed-shell systems. In this formalism scalar relativistic TDDFT calculations are first performed to determine the lowest single-group excited states and the spin-orbit coupling operator is applied to these single-group excited states to obtain the excitation energies with spin-orbit coupling effects included. The computational effort of the present method is much smaller than that of the two-component TDDFT formalism and this method can be applied to medium-size systems containing heavy elements. The compositions of the double-group excited states in terms of single-group singlet and triplet excited states are obtained automatically from the calculations. The calculated excitation energies based on the present formalism show that this formalism affords reasonable excitation energies for transitions not involving 5p and 6p orbitals. For transitions involving 5p orbitals, one can still obtain acceptable results for excitations with a small truncation error, while the formalism will fail for transitions involving 6p orbitals, especially 6p1/2 spinors.

Journal Article↗
PubMed2005

Density-functional calculations of relativistic spin-orbit effects on nuclear magnetic shielding in paramagnetic molecules.

Terms arising from the relativistic spin-orbit effect on both hyperfine and Zeeman interactions are introduced to density-functional theory calculation of nuclear magnetic shielding in paramagnetic molecules. The theory is a generalization of the former nonrelativistic formulation for doublet systems and is consistent to O(alpha4), the fourth power of the fine structure constant, for the spin-orbit terms. The new temperature-dependent terms arise from the deviation of the electronic g tensor from the free-electron g value as well as spin-orbit corrections to hyperfine coupling tensor A, the latter introduced in the present work. In particular, the new contributions include a redefined isotropic pseudocontact contribution that consists of effects due to both the g tensor and spin-orbit corrections to hyperfine coupling. The implementation of the spin-orbit terms makes use of all-electron atomic mean-field operators and/or spin-orbit pseudopotentials. Sample results are given for group-9 metallocenes and a nitroxide radical. The new O(alpha4) corrections are found significant for the metallocene systems while they obtain small values for the nitroxide radical. For the isotropic shifts, none of the three beyond-leading-order hyperfine contributions are negligible.

Journal Article↗
PubMed1979

Density matrix method for orbital localization.

A method is presented for localizing molecular orbitals, based on diagonalizing subunits of the density matrix. First, nonbonding orbitals are found by diagonalizing the monatomic subunits; then, diatomic sigma or pi bonding and antibonding orbitals are obtained from the diatomic subunits for all bonded pairs of atoms; finally, the delocalized pi-orbitals for particular chromophores are found by projecting the first set out of the self-consistent field (SCF) Hamiltonian. The results show good general agreement with other localization methods, with advantages in the ability to display group orbitals in complex molecules which most closely resemble the SCF orbitals for simple prototypes.

Journal Article↗
PubMed1998

Orbital hydatid cyst: an unusual presentation.

PURPOSE. To describe an unusually large and long-standing hydatid cyst of the orbit causing gross disfigurement of the eyeball. METHODS. Detailed investigations, consisting of radiological and hematological studies, were carried out to determine the cause of the unusually severe and long-standing proptosis. The patient underwent orbital exploration for the presumed diagnosis of orbital echinococcosis.The entire cyst with the globe was removed and sent for histopathological examination. RESULTS. The gross and histopathological findings of the specimen removed surgically confirmed the diagnosis of orbital hydatid cyst. CONCLUSION. The diagnosis of orbital hydatid cyst should be considered in unilateral severe proptosis of long duration with gross disfigurement of the globe and orbital walls.

Journal Article↗
PubMed1998

Malignant orbital and orbitomaxillary tumors: surgical considerations.

Malignant tumors of the orbit and the orbitomaxillary region constitute 4-8% of head and neck malignancies. The lesions can be primary orbital malignant tumors or can invade the orbit from the eyelids, the eyeball or the paranasal sinuses, especially the maxillary sinus and ethmoids. The commonest primary malignant tumors of the orbit are lymphomas, rhabdomyosarcomas and lacrimal gland epithelial tumors. These tumors are excluded from the present study since their management differs from that of metastatic tumors. Our experience is based on a series of 48 patients operated during the last five years. There was an equal distribution according to both age and sex, with two-thirds of the patients being over 60 years of age. Histologically, the basal cell carcinomas (B.C.C.) prevailed with 19 cases, followed by squamous cell carcinomas (Sq.C.C.) in 12, adenocarcinomas (AdenoCa) in 10 and orbital melanomas (O.M.) in 7. In 13 cases the maxilla was also affected. Surgical treatment varied from exenteration to wide cran iofacial resections; immediate reconstruction followed in all cases. Only 10 patients were treated with surgery alone. In the remaining 38 patients radiotherapy was given, alone or in combination with chemotherapy. The surgical techniques included exente ration with split-thickness skin grafting in 19 cases, exenteration with coverage with median forehead flap in 16, and maxillectomy with forehead and temporalis flaps in 7 cases. The tumors recurred in 12 patients, all of them in the first postoperative year. Ten patients died from intracranial involvement or distant metastases. In six of these patients the lesions were Sq.C.C., in two AdenoCa and in two O.M. It is concluded that the surgical treatment of orbital and orbitomaxillary malignancies, although subject to broad guidelines that determine the operability of the tumors, should be individualized according to the extent of the lesion and the experience of the surgeon.

Journal Article↗
PubMed1999

Hydatid cysts of the orbit in Xinjiang: a review of 18 cases.

PURPOSE To review the prevalence of orbital hydatid cyst in Xinjiang, China. METHOD. In the records of our hospital and in the issues of Chinese medical journals between 1956 and 1994, we found 18 cases of orbital hydatid cyst, including 10 cases from our hospital, two cases from the ShiHeZi Medical College, three cases from the YiLi local clinical hospital, and three other cases from the HeTian, WuSu and Changji local hospitals. All cases were verified by operation. RESULTS. In our hospital, a review of 3736 cases of hydatid cyst between 1957 and 1992 showed that hydatid cyst of the orbit accounted for 0.3%. Among the 18 cases, 7 were males and 11 females; the age ranged from 3 to 55 years and 15 cases were under 16 years of age (83%).The main symptom of orbital hydatid cyst was proptosis. Before the 1970s, the diagnosis depended on positive serological tests, X-ray examination and a history of infection of other parts of body with Echinococcus granulosus, with final confirmation by operation. In recent years, CT and ultrasonography have made possible a positional and qualitative diagnosis before surgery. With regard to the serological tests, the Intradermal test (ID) was positive in 77% of cases, while Indirect hemagglutination (IHA) and Counter-immuno-electrophoresis (CIEP) were positive in two cases and negative in two cases, respectively. No recurrence was seen when two cases were examined by CT six years after the operation, nor in eight other cases followed by letter for between 8 and 11 years. CONCLUSIONS. Hydatid cyst is an endemic disease in Xinjiang, but orbital hydatid cyst is rarely seen. The diagnosis is relatively easy to make in endemic countries, based on the clinical features, ultrasonography, CT-scan and serology. The main treatment for orbital hydatid cyst is surgery.

Journal Article↗
PubMed2000

Magnetic resonance imaging of the orbit: Basic principles and anatomy.

This review article gives a basic introduction to the technical principles of magnetic resonance imaging for ophthalmologists and orbital surgeons and describes the anatomical structures that can be identified on high-resolution magnetic resonance images of the orbit. The meaning of general imaging parameters, specific weighting of the images, and the use of contrast agents, fat suppression techniques and surface coils is explained. Possible artifacts are also described. The advantages and disadvantages of MRI in comparison with computed tomography (CT) are discussed in order to give recommendations for the use of the appropriate imaging modality in patients with orbital disorders. Apart from delineating the course of the extraocular muscles, high-resolution MRI is able to depict not only all important blood vessels and cranial nerves of the orbit but also major septa of the orbital connective tissue system. Clinical applications are also mentioned to show that high-resolution MRI may contribute to a specific diagnosis in orbital disease.

Journal Article↗
PubMed2001

Orbital amputation neuroma causing failure of prosthesis wear.

PURPOSE. To describe an orbital amputation neuroma that developed following enucleation and led to the patient 's inability to wear an oc- ular prosthesis. METHODS. This is a retrospective case report in a private practice setting. An elderly woman underwent enucleation of the right eye,and subsequently developed orbital pain and inflammation. Systemic and local steroids proved of no benefit, and the socket became increasingly painful,contracted and frozen. She was unable to wear her prosthesis. An orbital mass was noted,and subsequently biopsied. RESULTS. The biopsy specimen demonstrated orbital amputation neuroma. Her pain was relieved. CONCLUSION. Orbital amputation neuroma should be a diagnostic con- sideration when a patient develops a painful orbital mass following enucleation.

Journal Article↗
PubMed1988

UV photoelectron spectroscopy and ab initio characterization of valence orbital structures and conformations of neutral phosphate esters.

The HeI UV photoelectron spectrum of trimethyl phosphate (TMP) has been measured and interpreted with the aid of SCF molecular orbital calculations carried out with STO-3G, STO-3G* and 4-31G basis functions. The photoelectron spectrum of TMP is more accurately reproduced by results from 4-31G calculations than by results from STO-3G or STO-3G* calculations. However, all three basis sets yield results which predict the same assignment of the photoelectron spectrum. Results at the 4-31G level indicate that whether calculations are based on crystallographic bond angles and bond lengths or on STO-3G optimized geometries has little effect on the energetic ordering of the upper occupied orbitals. The energetic ordering of orbitals is also found to be only weakly dependent upon the torsional angle phi, describing rotation of ester groups about P-O bonds and upon the torsional angle psi, describing rotation of methyl groups about C-O bonds. For trimethyl phosphate, with C3 symmetry, the vertical ionization potentials of the upper occupied orbitals are 10.81 eV (8e), 11.4 eV (9a), 11.93 eV (7e), 12.6-12.9 eV (8a and 6e), 14.4 eV (7a) and 15.0-16.0 eV (5e and 6a). Calculations at the 4-31G level indicate that many of the highest occupied orbitals in neutral dimethyl phosphate and methyl phosphate have energies and electron distributions similar to orbitals in TMP. For TMP, a search for optimized values of phi and psi has been carried out at the STO-3G*level. In agreement with previous NMR studies and with classical potential calculations, the STO-3G* results indicate that both the gauche (phi = 53.1 degrees) and anticlinal (phi = 141.9 degrees) conformations are thermally accessible. Also in agreement with the classical potential calculations, the STO-3G* results predict that in the all gauche conformation energy is minimized when the methyl groups assume a staggered geometry (psi = 60 degrees to 80 degrees) and that an energy maximum occurs for an eclipsed geometry (phi = 0 degrees to 20 degrees). A study of the dependence of optimized values of O-P-O ester bond angles on the torsional angles, phi, was carried out at the STO-3G, STO-3G* and 4-31G levels. The results demonstrate that for C3 symmetry, the coupling of O-P-O angles to phi is influence by repulsive steric interactions.

Chemical Phenomena↗
PubMed1998

Thyrotropin receptor expression in cultured Graves' orbital preadipocyte fibroblasts is stimulated by thyrotropin.

Our laboratory has shown recently that the thyrotropin receptor (TSHr) is expressed in orbital adipose/connective tissues from patients with Graves' ophthalmopathy (GO), and that this receptor is not demonstrable in orbital tissues from normal individuals. In order to study the regulation of TSHr expression in the orbit in GO, we treated cultures of Graves' orbital preadipocyte fibroblasts with the TSHr ligand thyrotropin (TSH; 100 mU/L). We found increased expression of both intact (2.4 kb) and variant (1.3 kb) TSHr mRNA and of TSHr protein in orbital fibroblasts following 72 hr treatment with TSH. These studies suggest that the expression of this receptor in the orbit in vivo may be stimulated by TSH or other TSHr ligands, and that this stimulation may be important in the development of GO.

Adipocytes↗
PubMed2001

Sentinel node biopsy for orbital and ocular adnexal tumors.

PURPOSE: To describe a technique for sentinel node mapping and biopsy in patients with orbital or adnexal tumors. METHODS: Five patients with orbital and adnexal tumors were studied. Two patients had malignant eyelid melanomas (one of the skin and one of the conjunctiva), one with orbital invasion. Two patients had sebaceous gland carcinoma, and one patient had a mucoepidermoid carcinoma of the conjunctiva; 500 microCi of Technetium-99m sulfur nanocolloid (Nycomed Amersham, Princeton, NJ) diluted to 1.0 mL was injected intradermally at the lateral canthus. The patients were positioned as they would be during surgery. Lymphoscintigraphy was performed by means of anterior, lateral, and oblique views. The tracer was followed to the first lymphatic basin, and the sentinel node was identified. Cutaneous markers were placed to denote the site. During surgery, lymphoscintigraphy scans and a hand-held gamma probe were used to locate the sentinel node. Once excised, the sentinel node was sent for histopathology. Frozen sectioning confirmed the presence of lymphoid tissue. Permanent sections with immunohistochemical markers were performed to examine for metastatic disease. RESULTS: The sentinel node biopsy technique was applied to 5 patients with orbital and adnexal tumors. All lymph nodes were free of tumor on histopathologic examination. CONCLUSIONS: Sentinel node mapping and biopsy are possible for orbital and adnexal tumors. The morbidity of elective lymph node dissection and adjuvant radiotherapy can be avoided. Our results are preliminary, and further work must be done to identify the lymphatic basins of the orbit and ocular adnexa.

Adenocarcinoma, Sebaceous↗
PubMed2006

Aesthetic management of the nasal component of naso-orbital ethmoid fractures.

LEARNING OBJECTIVES: After studying this article, the participant should be able to: 1. Discuss the critical anatomic structures of the nose that are affected in naso-orbital ethmoid fractures. 2. Discuss the advantages of early, complete nasal reconstruction of these fractures. 3. Apply a clinical algorithm to such nasal reconstruction. 4. List the techniques used in aesthetic reconstruction of the nose in naso-orbital ethmoid fractures. BACKGROUND: Fractures of the naso-orbital ethmoid complex pose challenging management issues. Although basic treatment principles have been well described, the aesthetic management of the nasal component has not been adequately addressed in the literature. METHODS: When secondary nasal deformities occur, they are difficult to correct. Optimal primary correction of the nasal deformity is accomplished using the following four principles: (1) rigid fixation of the nasal pyramid and restoration of nasal height and length; (2) restoration of tip projection; (3) septal reduction/reconstruction; and (4) lateral nasal wall augmentation. RESULTS: Successful management of naso-orbital ethmoid fractures is a complex and challenging task. Both the bony and soft-tissue components must be addressed and the extent of the injury must be adequately diagnosed to avoid omission of critical steps in the reconstruction. Inadequate treatment of naso-orbital ethmoid fractures can produce a severe cosmetic deformity that is very difficult to correct secondarily. CONCLUSION: The authors discuss the nasal component of naso-orbital ethmoid complex injuries and detail the key principles in their algorithm for aesthetic nasal reconstruction.

Algorithms↗
PubMed2001

Periodic orbits in Hamiltonian chaos of the annular billiard.

We consider the motion of trajectories in the annular billiard, constituted of a circle with an internal, perfectly reflecting, eccentrically located secondary circle, displaying a generic Hamiltonian behavior (including periodic orbits, invariant curves, and chaotic areas). Periodic orbits embedded in the phase space are systematically investigated, with a focus on inclusion-touching periodic orbits, up to symmetrical orbits of period 6. Candidates for periodic orbits are detected by investigating grayscale distance charts and, afterward, each candidate is validated (or rejected) by using analytical and/or numerical methods. This Hamiltonian problem with Hamiltonian chaos (mechanical language) may equivalently be viewed as an optical problem with optical chaos (expressed with a geometrical optics language). It then may be extended to the study of interaction between a laser beam (or a plane wave as a limit) and a sphere with an eccentrically located spherical inclusion, this interaction being described by a generalized Lorenz-Mie theory recently established. Inclusion-touching periodic orbits in the annular billiard may generate a new class of morphology-dependent resonances in the associated extended generalized Lorenz-Mie theory problem.

Journal Article↗
PubMed2004

Analysis of orbital decay time for the classical hydrogen atom interacting with circularly polarized electromagnetic radiation.

Here we show that a wide range of states of phases and amplitudes exist for a circularly polarized (CP) plane wave to act on a classical hydrogen model to achieve infinite times of stability (i.e., no orbital decay due to radiation reaction effects). An analytic solution is first deduced to show this effect for circular orbits in the nonrelativistic approximation. We then use this analytic result to help provide insight into detailed simulation investigations of deviations from these idealistic conditions. By changing the phase of the CP wave, the time t(d) when orbital decay sets in can be made to vary enormously. The patterns of this behavior are examined here and analyzed in physical terms for the underlying but rather unintuitive reasons for these nonlinear effects. We speculate that most of these effects can be generalized to analogous elliptical orbital conditions with a specific infinite set of CP waves present. The paper ends by briefly considering multiple CP plane waves acting on the classical hydrogen atom in an initial circular orbital state, resulting in "jump-like" and "diffusion-like" orbital motions for this highly nonlinear system. These simple examples reveal the possibility of very rich and complex patterns that occur when a wide spectrum of radiation acts on this classical hydrogen system.

Journal Article↗
PubMed2006

Measure of orbital stickiness and chaos strength.

Patterns can be used effectively to characterize dynamical orbits as regular or chaotic. The proposed method focuses on local, epochal characterization of orbits as opposed to global characterization usually employed by most established measures. The "patterns method" provides essentially a measure of chaos strength for every extremum of a signal. For this reason, it provides information about sticky epochs of chaotic orbits, as well as time-dependent orbits. This way it can be used to give extremely detailed pictures of the phase space of a system, as well as to provide characterizations early in the evolution of orbits. Moreover, the method applies generally; all that is required is a signal, of which an orbit is merely an example.

Journal Article↗
PubMed2000

Orbital liquid in three-dimensional mott insulator: LaTiO3

We present a theory of spin and orbital states in Mott insulator LaTiO3. The spin-orbital superexchange interaction between d(1)(t(2g)) ions in cubic crystal suffers from a pathological degeneracy of orbital states at the classical level. Quantum effects remove this degeneracy and result in the formation of the coherent ground state, in which the orbital moment of t(2g) level is fully quenched. We find a finite gap for orbital excitations. Such a disordered state of local degrees of freedom on unfrustrated, simple cubic lattice is highly unusual. Orbital liquid state naturally explains observed anomalies of LaTiO3.

Journal Article↗
PubMed2002

Quantum behavior of orbitals in ferromagnetic titanates: novel orderings and excitations.

We investigate the collective behavior of orbital angular momentum in the spin ferromagnetic state of a Mott insulator with t(2g) orbital degeneracy. The frustrated nature of the interactions leads to an infinite degeneracy of classical states. Quantum effects select four distinct orbital orderings. Two of them have a quadrupolar order, while the other states show in addition weak orbital magnetism. Specific predictions are made for neutron scattering experiments which might help to identify the orbital order in YTiO3 and to detect the elementary orbital excitations.

Journal Article↗
PubMed2003

Orbital-order-induced metal-insulator transition in La(1-x)Ca(x)MnO3.

We present evidence that the insulator-to-metal transition in La(1-x)Ca(x)MnO3 near x approximately 0.2 is driven by the suppression of coherent Jahn-Teller distortions, originating from d-type orbital ordering. The orbital-ordered state is characterized by large long-range Q2 distortions below T(O'- O*). Above T(O'- O*) we find evidence for coexistence between an orbital-ordered and an orbital-disordered state. This behavior is discussed in terms of electronic phase separation in an orbital-ordered insulating and an orbital-disordered metallic state.

Journal Article↗