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At least 793 records · Page 44Linked to original sources
PubMed2004

Spin-orbit-induced anomalous pH-dependence in (1)H NMR spectra of Co(III) amine complexes: a diagnostic tool for structure elucidation.

The pH-dependent (1)H NMR characteristics of a series of Co(III)-(polyamin)-aqua and Co(III)-(polyamin)-(polyalcohol) complexes, [Co(tach)(ino-kappa(3)-O(1,3,5))](3+) (1(3+)), [Co(tach)(ino-kappa(3)-Omicron(1,2,6))](3+) (2(3+)), [Co(tach)(taci-kappa-Nu(1)-kappa(2)-O(2,6))](3+) (3(3+)), [Co(ditame)(H(2)O)](3+) (4(3+)), and [Co(tren)(H(2)O)(2)](3+) (5(3+)), were studied in D(2)O by means of titration experiments (tach = all-cis-cyclohexane-1,3,5-triamine, ino = cis-inositol, taci = 1,3,5-triamino-1,3,5-trideoxy-cis-inositol, tren = tris(2-aminoethyl)amine, ditame = 2,2,6,6-tetrakis-(aminomethyl)-4-aza-heptane). A characteristic shift was observed for H(-C) hydrogen atoms in the alpha-position of a coordinated amino group upon deprotonation of a coordinated oxygen donor. For a cis-H-C-N-Co-O-H arrangement, deprotonation of the oxygen donor resulted in an additional shielding (shift to lower frequency) of the H(-C) proton, whereas for a trans-H-C-N-Co-O-H arrangement, deprotonation resulted in a deshielding (shift to higher frequency). The effect appears to be of rather general nature: it is observed for primary (1(3+)-5(3+)), secondary (4(3+)), and tertiary (5(3+)) amino groups, and for the deprotonation of an alcohol (1(3+)-3(3+)) or a water (4(3+), 5(3+)) ligand. Spin-orbit-corrected density functional calculations show that the high-frequency deprotonation shift for the trans-position is largely caused by a differential cobalt-centered spin-orbit effect on the hydrogen nuclear shielding. This effect is conformation dependent due to a Karplus-type behavior of the spin-orbit-induced Fermi-contact shift and thus only significant for an approximately antiperiplanar H-C-N-Co arrangement. The differential spin-orbit contribution to the deprotonation shift in the trans-position arises from the much larger spin-orbit shift for the protonated than for the deprotonated state. This is in turn due to a trans-effect of the deprotonated (hydroxo or alkoxo) ligand, which weakens the trans Co-N bond and thereby interrupts the Fermi-contact mechanism for transfer of the spin-orbit-induced spin polarization to the hydrogen nucleus in question. The unexpectedly large long-range spin-orbit effects found here for 3d metal complexes are traced back to small energy denominators in the perturbation theoretical expressions of the spin-orbit shifts.

Journal Article↗
PubMed2001

Orbits in the H(2)O molecule.

We study the forms of the orbits in a symmetric configuration of a realistic model of the H(2)O molecule with particular emphasis on the periodic orbits. We use an appropriate Poincare surface of section (PSS) and study the distribution of the orbits on this PSS for various energies. We find both ordered and chaotic orbits. The proportion of ordered orbits is almost 100% for small energies, but decreases abruptly beyond a critical energy. When the energy exceeds the escape energy there are still nonescaping orbits around stable periodic orbits. We study in detail the forms of the various periodic orbits, and their connections, by providing appropriate stability and bifurcation diagrams. (c) 2001 American Institute of Physics.

Journal Article↗
PubMed1999

Global analysis of periodic orbit bifurcations in coupled Morse oscillator systems: time-reversal symmetry, permutational representations and codimension-2 collisions.

In this paper we study periodic orbit bifurcation sequences in a system of two coupled Morse oscillators. Time-reversal symmetry is exploited to determine periodic orbits by iteration of symmetry lines. The permutational representation of Tsuchiya and Jaffe is employed to analyze periodic orbit configurations on the symmetry lines. Local pruning rules are formulated, and a global analysis of possible bifurcation sequences of symmetric periodic orbits is made. Analysis of periodic orbit bifurcations on symmetry lines determines bifurcation sequences, together with periodic orbit periodicities and stabilities. The correlation between certain bifurcations is explained. The passage from an integrable limit to nointegrability is marked by the appearance of tangent bifurcations; our global analysis reveals the origin of these ubiquitous tangencies. For period-1 orbits, tangencies appear by a simple disconnection mechanism. For higher period orbits, a different mechanism involving 2-parameter collisions of bifurcations is found. (c) 1999 American Institute of Physics.

Journal Article↗
PubMed2004

Decomposition of nuclear magnetic resonance spin-spin coupling constants into active and passive orbital contributions.

The theory of the J-OC-PSP (decomposition of J into orbital contributions using orbital currents and partial spin polarization) method is derived to distinguish between the role of active, passive, and frozen orbitals on the nuclear magnetic resonance (NMR) spin-spin coupling mechanism. Application of J-OC-PSP to the NMR spin-spin coupling constants of ethylene, which are calculated using coupled perturbed density functional theory in connection with the B3LYP hybrid functional and a [7s,6p,2d/4s,2p] basis set, reveal that the well-known pi mechanism for Fermi contact (FC) spin coupling is based on passive pi orbital contributions. The pi orbitals contribute to the spin polarization of the sigma orbitals at the coupling nuclei by mediating spin information between sigma orbitals (spin-transport mechanism) or by increasing the spin information of a sigma orbital by an echo effect. The calculated FC(pi) value of the SSCC (1)J(CC) of ethylene is 4.5 Hz and by this clearly smaller than previously assumed.

Journal Article↗
PubMed2004

Variationally optimized basis orbitals for biological molecules.

Numerical atomic basis orbitals are variationally optimized for biological molecules such as proteins, polysaccharides, and deoxyribonucleic acid within a density functional theory. Based on a statistical treatment of results of a fully variational optimization of basis orbitals (full optimized basis orbitals) for 43 biological model molecules, simple sets of preoptimized basis orbitals classified under the local chemical environment (simple preoptimized basis orbitals) are constructed for hydrogen, carbon, nitrogen, oxygen, phosphorous, and sulfur atoms, each of which contains double valence plus polarization basis function. For a wide variety of molecules we show that the simple preoptimized orbitals provide well convergent energy and physical quantities comparable to those calculated by the full optimized orbitals, which demonstrates that the simple preoptimized orbitals possess substantial transferability for biological molecules.

Biophysics↗
PubMed2000

Effect of prior orbital decompression on outcome of strabismus surgery in patients with thyroid ophthalmopathy.

PURPOSE: To compare strabismus surgery outcomes of patients who have had prior orbital decompression for thyroid ophthalmopathy with those of patients who have not had decompression. METHODS: The records of all patients operated on by the author for strabismus related to thyroid ophthalmopathy were retrospectively reviewed. RESULTS: Fifty patients were included in this study. Seventeen patients had previously undergone orbital decompression, and 33 patients had not. Seventy-six percent of patients who had had orbital decompression had a good or excellent outcome compared with 91% of those who had not had orbital decompression. Patients in the orbital decompression group had an average of 1.4 operations compared with 1.2 in the no-decompression group. The average numbers of muscles operated on were 3.1 in the decompression group and 1.9 in the no-decompression group. Patients who had been decompressed were more than 4 times as likely to require surgery for both a horizontal and vertical deviation than patients who had not been decompressed. CONCLUSIONS: Patients with thyroid ophthalmopathy who have had orbital decompression have a lower success rate of surgery for strabismus, more frequently need correction for both horizontal and vertical deviations, and have more muscles operated on than patients who have not had orbital decompression. The need for orbital decompression in patients with Graves' disease is reflective of a worse degree of orbitopathy. In addition, ocular changes from decompression surgery may interfere with a successful result from strabismus surgery.

Decompression, Surgical↗
PubMed2004

Incidence of postblepharoplasty orbital hemorrhage and associated visual loss.

PURPOSE: Orbital hemorrhage, especially when associated with visual loss, is a significant complication of cosmetic eyelid surgery. We investigated the incidence of this complication among cases handled by members of the American Society of Ophthalmic Plastic and Reconstructive Surgery. We also reviewed the length of time between surgery and the onset of bleeding and sought any factors that may contribute to these cases. METHODS: A 2-page questionnaire was sent to all American Society of Ophthalmic Plastic and Reconstructive Surgery members. Responses were tabulated as to total numbers of cases performed, the incidence of postoperative orbital hemorrhage, treatments, and incidence of permanent visual loss. Comorbidities were also reviewed. RESULTS: Two hundred thirty-seven responses were received from American Society of Ophthalmic Plastic and Reconstructive Surgery members, collectively representing 269,433 cases. Among these cases, there were 149 orbital hemorrhages, 48 cases associated with temporary visual loss, and 12 cases associated with permanent visual loss. The majority of these cases occurred within the first 3 hours of surgery, and the risk decreased significantly after 24 hours after surgery. Common comorbidities were hypertension, perioperative aspirin use, postoperative vomiting, and increased physical activity. Treatment commonly consisted of wound drainage with cauterization of active bleeders, lateral canthotomy, intravenous steroids, and intraocular pressure-lowering drugs. Orbital decompression was infrequently used; anterior chamber paracentesis was not used. This study is limited by recall biases regarding the number of cases performed by each responding surgeon and the number of relevant cases of orbital hemorrhage. CONCLUSIONS: The incidence of orbital hemorrhage associated with cosmetic eyelid surgery is 0.055% (1:2,000), and orbital hemorrhage with permanent visual loss is 0.0045% (1:22,000) [corrected] Development of orbital hemorrhage is most common within the first 24 hours after surgery, especially within the first 0 to 3 hours, but can occur as late as several days after surgery.

Blepharoplasty↗
PubMed2002

Orbital ordering in frustrated Jahn-Teller systems with 90 degrees exchange.

We show that superexchange interactions in frustrated Jahn-Teller systems with transition metal ions connected by the 90 degrees metal-oxygen-metal bonds (e.g., NaNiO2, LiNiO2, and ZnMn2O4) are much different from those in materials with the 180 degrees bonds. In the 90 degrees -exchange systems spins and orbitals are decoupled: the spin exchange is much weaker than the orbital one and it is ferromagnetic for all orbital states. Though the mean-field orbital ground state is strongly degenerate, quantum orbital fluctuations select particular ferro-orbital states. We explain the orbital and magnetic ordering observed in NaNiO2 and show that LiNiO2 is not a spin-orbital liquid.

Journal Article↗
PubMed2004

Field-induced orbital and magnetic phases in Ca3Ru2O7.

Magnetic-field- and temperature-dependent Raman scattering studies of Ca3Ru2O7 reveal dramatic field-dependent properties arising from transitions between various complex orbital and magnetic phases, including a field-induced orbital-ordered to orbital-disordered transition (H(o) // hard axis), and a reentrant orbital-ordered to orbital-disordered to orbital-ordered transition (H(o) // easy axis). We find that the dramatic magnetic-field properties are most prevalent in a "mixed"-magnetic and -orbital phase regime, providing evidence for a strong connection between orbital phase inhomogeneity and "colossal" field effects in the ruthenates.

Journal Article↗
PubMed2005

Efficient orbit integration by manifold correction methods.

Triggered by a desire to investigate, numerically, the planetary precession through a long-term numerical integration of the solar system, we developed a new formulation of numerical integration of orbital motion named manifold correct on methods. The main trick is to rigorously retain the consistency of physical relations, such as the orbital energy, the orbital angular momentum, or the Laplace integral, of a binary subsystem. This maintenance is done by applying a correction to the integrated variables at each integration step. Typical methods of correction are certain geometric transformations, such as spatial scaling and spatial rotation, which are commonly used in the comparison of reference frames, or mathematically reasonable operations, such as modularization of angle variables into the standard domain [-pi, pi). The form of the manifold correction methods finally evolved are the orbital longitude methods, which enable us to conduct an extremely precise integration of orbital motions. In unperturbed orbits, the integration errors are suppressed at the machine epsilon level for an indefinitely long period. In perturbed cases, on the other hand, the errors initially grow in proportion to the square root of time and then increase more rapidly, the onset of which depends on the type and magnitude of the perturbations. This feature is also realized for highly eccentric orbits by applying the same idea as used in KS-regularization. In particular, the introduction of time elements greatly enhances the performance of numerical integration of KS-regularized orbits, whether the scaling is applied or not.

Journal Article↗
PubMedDate not supplied

Temporoparietal fascial flap in orbital reconstruction.

OBJECTIVE: To evaluate the success of the temporoparietal fascial flap (TPFF) in the primary or secondary reconstruction of difficult orbital defects and to review the surgical techniques. DESIGN: Retrospective analysis. SETTING: Tertiary medical center. PATIENTS: Nine patients with diverse orbital cavity or periorbital soft tissue and bony defects due to trauma, benign or malignant neoplasms, and radiation treatment. INTERVENTIONS: Temporoparietal fascial flap anatomy and techniques of harvest and inset are reviewed in detail. Four cases are presented to illustrate possible variables in orbital reconstruction. Variables examined include the location of defects, the success of flap survival in orbital cavities after primary or secondary reconstruction, the effects of prior irradiation on flap survival, and the possibility of concurrent osteointegrated implant placement with TPFF reconstruction. MAIN OUTCOME MEASURES: Functional and aesthetic outcomes were determined by physical examination and preoperative and postoperative photographs. RESULTS: All patients had successful transfer of TPFF grafts without flap compromise. Temporoparietal fascial flap was a viable option for subtle orbital and malar contour defects. In chronically inflamed wounds such as with osteoradionecrosis and orbitoantral fistula, TPFF successfully restored vascularity, obliterated the defects, and enabled the placement of osteointegrated implants. The TPFF also supported the concurrent placement of a free calvarial bone graft. Finally, split-thickness skin grafted onto a pedicled TPFF showed 100% survival. CONCLUSIONS: The TPFF is one of the most reliable and versatile regional flaps in the head and neck for orbital reconstruction. This study presents the use of TPFF in a variety of orbital defects, from lateral bony rim defects to total exenteration. Timing of repair in this study spans from immediate reconstruction to reconstruction delayed more than 50 years after the initial injury. In all cases, reconstruction with TPFF resulted in improved bony and soft tissue contours, and incurred minimal morbidity.

Adult↗
PubMed1989

Cerebrospinal fluid leakage complicating orbital exenteration.

In three cases of cerebrospinal fluid leakage complicating orbital exenteration, leakage occurred intraoperatively following relatively low-power (0 to 25 W), high-frequency monopolar cautery to the orbital roof. Six cadaver orbits and 25 dried skulls were examined to investigate possible causes of intraoperative cerebrospinal fluid leakage. In this experimental model, monopolar cautery to the orbital roof did not cause cerebrospinal fluid leakage; however, cautery to preexistent foramina or experimentally created defects in the orbital bones did. In exenteration, monopolar cautery may transmit thermal energy through extant body defects in the orbital roof directly to the dura, resulting in its disruption. These defects may be congenital, tumor related, or iatrogenic. Alternative methods of hemostasis should probably be employed to control bleeding that occurs along the orbital roof during exenteration.

Aged↗
PubMed1999

Endoscopic endonasal repair of orbital floor fracture.

BACKGROUND: High-resolution endoscopes and the advent of endoscopic instruments for sinus surgery provide surgeons with excellent endonasal visualization and access to the orbital walls. OBJECTIVE: To demonstrate repair of orbital floor blowout fractures through an intranasal endoscopic approach that allows repair of the orbital floor fracture and elevation of the orbital content using a balloon catheter without an external incision. DESIGN: This study was a retrospective analysis of 11 patients who underwent surgical repair of orbital floor fractures from September 1994 to June 1997. There were 10 male patients and 1 female patient, aged 12 to 32 years (mean age, 24 years). These patients had undergone primary repair of pure orbital blowout fractures and were followed up at least 6 months after surgery. RESULTS: There were no intraoperative or postoperative complications. Nine patients showed a complete improvement of their diplopia. Two patients with posterior fractures showed persistent diplopia, which was well managed by prisms. CONCLUSION: Endoscopic repair of the orbital floor blowout fracture using an endonasal approach appears to be a safe and effective technique for the treatment of diplopia.

Adolescent↗
PubMed2006

Bilateral orbital emphysema and pneumocephalus as a result of accidental compressed air exposure.

Orbital emphysema is a rare condition in the absence of trauma or sinus disease. A 22-year-old man suffering from left orbital trauma due to sudden exposure to compressed air tube was admitted with severe pain in the left eye, swelling, and mild periorbital ecchymosis. Physical examination revealed a large conjunctival laceration in the left orbit. Multislice computed tomographic scanning of the head and orbits showed extensive radiolucencies consistent with the air in both orbits, more prominent in the left. There was also subcutaneous air in the left periorbital soft tissue extending through fronto-temporal and zygomatic areas. Air was also demonstrated adjacent to the left optic canal and within the subarachnoid space intracranially. There was no evidence of any orbital, paranasal sinus, or cranial fracture. Visual acuity was minimally decreased bilaterally. The conjunctiva was sutured under local anesthesia. After 3 weeks of follow-up, the patient completely recovered without visual loss. Bilateral orbital emphysema with pneumocephalus can occur from a high-pressure compressed air injury after unilateral conjunctival trauma without any evidence of fracture.

Adult↗
PubMed2005

Frameless image-guided neuronavigation in orbital surgery: practical applications.

Frameless neuronavigation has been increasingly used in intracranial and spinal neurosurgery. However, the application of neuronavigation in orbital surgery has not yet been reported. The purpose of this study was to evaluate whether frameless navigation in the orbit provides sufficient clinical application accuracy and thus a useful tool in orbital surgery. A frameless infrared-based neuronavigation system (VectorVision, BrainLAB, Heimstetten, Germany) was used in the microsurgical removal of 11 orbital tumors (five cavernomas, three lymphomas, two dermoid tumors, and one rhabdomyosarcoma). The transconjunctival approach was performed in seven cases, lateral orbitotomy in three cases, and the extradural pterional approach was performed in one case. The surgery was successful and without any complications in all cases. The registration accuracy of the neuronavigation was between 1.8 and 2.2 mm, with a mean of 1.9 mm. Subtotal tumor debulking was performed in one case with lymphoma. One patient was only biopsied due to suspected systemic lymphoma disease. Total removal of the tumor could be accomplished in the other nine patients. Image guidance during orbital surgery offered excellent three-dimensional guidance on the surface of the intraorbital lesions, allowing a safer, more controlled surgery. The surgical targets in the orbit are fixed structures, thus no shifting occurs and continuous high intraoperative navigation accuracy can be achieved. The use of the navigation clearly reduces the operative risk and increases the effectiveness of microsurgical orbital procedures.

Adult↗
PubMed1985

Radiotherapy of lymphoid diseases of the orbit.

Thirty-two patients with orbital pseudotumor (18), reactive lymphoid hyperplasia (2), atypical lymphoid infiltrate (4) or malignant lymphoma (8) were treated in the Division of Radiation Therapy at Stanford University between January 1973 and May 1983. Of the 20 patients with pseudotumor or reactive lymphoid hyperplasia, 10 had unilateral lesions and 10 had bilateral lesions. Biopsy samples were obtained in 15 patients; in five patients with bilateral disease the diagnosis was made on the basis of computed tomography (CT) and clinical findings. The majority of patients were referred because of disease refractory to treatment with corticosteroids. The patients were given a mean dose of 2360 rad using complex, individualized megavoltage techniques including lens shielding. Radiotherapy was well tolerated with no significant acute or late complications. Fifteen patients had complete resolution of symptoms after treatment; five had continued symptoms. Of the 12 patients with malignant lymphoma or atypical lymphoid infiltrate, four had systemic lymphoma with orbital involvement and eight had orbital involvement only. The diagnosis was made by biopsy in all patients and immunophenotyping was done in six cases, of which 5 were monoclonal. Patients were evaluated with a chest radiograph, lymphogram or abdominal CT, bone marrow biopsy and orbital CT. A mean dose of 3625 rad was delivered to the orbit only. Most of the patients received complex megavoltage treatment using bolus. All patients in this group had a complete response and local control. There were no relapses in those with localized disease. Two patients developed cataracts. Carefully planned orbital radiotherapy provides local control without symptomatic sequelae for orbital masses ranging from pseudotumor to malignant lymphoma.

Adult↗
PubMed2006

Postmortem orbital findings in shaken baby syndrome.

PURPOSE: To compare postmortem orbital findings in pediatric accidental head injury to Shaken Baby Syndrome (SBS). DESIGN: Retrospective study. METHODS SETTING: Institutional. STUDY POPULATION: Thirty-six patients underwent postmortem modified exenteration with sectioning of the orbital contents; 18 victims of SBS and 18 cases of fatal accidental head trauma. OBSERVATION PROCEDURE: In all cases of children who died from accidental head trauma, the orbital tissues were separated to expose the optic nerve sheath. Patients with gross evidence of hemorrhage within the sheath were included. All cases of SBS were included. After accidental head injury, exenteration was performed only if optic nerve sheath hemorrhage was suspected on gross examination. All children younger than 18 years old with head injury as primary cause of death were included. SBS is defined as having at least two of the following: (1) typical abnormal findings on neuroimaging, (2) typical skeletal injury, (3) retinal hemorrhages, (4) history of abusive shaking with or without blunt head trauma, or (5) an inadequate history to explain the observed injuries. MAIN OUTCOME MEASURE: Presence or absence of orbital hemorrhage. RESULTS: Orbital tissue injury is more common in SBS than accidental head trauma without orbital fracture. In addition, optic nerve sheath and optic nerve intradural hemorrhage are also significantly more common in SBS (P < .0001). CONCLUSIONS: Our study reports new evidence of injury to orbital tissues in SBS and supports the concept that these finding are due to unique acceleration-deceleration forces of this type of abusive head injury.

Child, Preschool↗
PubMed2005

Diagnosis and treatment of retrobulbar haematomas following blunt orbital trauma: a description of eight cases.

Retrobulbar haematoma following blunt orbital trauma is a rare, but potentially serious, complication, since it can evolve rapidly from visual impairment to permanent loss of vision. This sight-threatening situation most commonly arises from orbital bleeding accompanying undisplaced fractures of the orbital walls, an event that increases the pressure inside the orbit and results in vascular damage to the optic nerve. The clinical presentation includes pain, exophthalmos with proptosis, and internal ophthalmoplegia, with impairment or loss of the pupillary reflex. A thin-layer orbital CT scan is an essential diagnostic aid. Any delay between the onset of symptoms and treatment can have a significant effect on functional recovery. Therapy is based on orbital decompression, via different surgical approaches, with the intention of reducing the pressure on the nerve and vascular structures inside the orbit. This paper presents eight cases of retrobulbar haematoma and their follow-up, in detail.

Adult↗