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Biomedical subjects

D Mihalache

Publications and source records attributed to D Mihalache.

At least 37 records · Page 2Linked to original sources
PubMed2000

Three-dimensional walking spatiotemporal solitons in quadratic media

Two-parameter families of chirped stationary three-dimensional spatiotemporal solitons in dispersive quadratically nonlinear optical media featuring type-I second-harmonic generation are constructed in the presence of temporal walk-off. Basic features of these walking spatiotemporal solitons, including their dynamical stability, are investigated in the general case of unequal group-velocity dispersions at the fundamental and second-harmonic frequencies. In the cases when the solitons are unstable, the growth rate of a dominant perturbation eigenmode is found as a function of the soliton wave number shift. The findings are in full agreement with the stability predictions made on the basis of a marginal linear-stability curve. It is found that the walking three-dimensional spatiotemporal solitons are dynamically stable in most cases; hence in principle they may be experimentally generated in quadratically nonlinear media.

Journal Article↗
PubMed2000

Azimuthal instability of spinning spatiotemporal solitons

We find one-parameter families of three-dimensional spatiotemporal bright vortex solitons (doughnuts, or spinning light bullets), in dispersive quadratically nonlinear media. We show that they are subject to a strong instability against azimuthal perturbations, similarly to the previously studied (2+1)-dimensional bright spatial vortex solitons. The instability breaks the spinning soliton into several fragments, each being a stable nonspinning light bullet.

Journal Article↗
PubMed1999

Exact solitary-wave solutions of chi(2) Ginzburg-Landau equations.

A family of exact temporal solitary-wave solutions (dissipative solitons) to the equations governing second-harmonic generation in quadratically nonlinear optical waveguides, in the presence of linear bandwidth-limited gain at the fundamental harmonic and linear loss at the second harmonic, is found, and the existence domain for the solutions is delineated. Direct numerical simulations of the solitons demonstrate that, as well as the classical pulse solutions to the cubic Ginzburg-Landau equation, the dissipative solitons can propagate robustly over a considerable distance before the model's intrinsic instability leads to onset of "turbulence." Two-soliton bound states are also predicted and then found in the direct simulations. We estimate real values of the physical parameters necessary for the existence of the solitons predicted, and conclude that they can be observed experimentally. A promising application for the solitons is their use in closed-loop cavities.

Journal Article↗
PubMed1999

Soliton generation in optical fibers for a dual-frequency input.

We analyze scenarios of soliton generation in an ideal fiber for an input that consists of either two in-phase or out-of-phase solitonlike optical pulses at different frequencies. In both cases the relationship between the structure of the emerging solitons and the frequency separation of the initial solitons is studied both analytically and numerically. Depending on the value of the frequency detuning, if the two initial solitons are in phase (symmetric input), two bound solitons with equal amplitudes (breather), a single soliton, or a pair of solitons, which have equal amplitudes and exhibit opposite velocities, can be generated. When the two initial solitons are out-of-phase (antisymmetric input), only the last scenario takes place. Also, we calculated the threshold values of the frequency separation at which the structure of the emerging solitons changes. Moreover, we demonstrated that two of these critical frequencies correspond to cusplike maxima of the energy density of the radiative modes. Finally, we show that these analytical results are entirely verified by numerical simulations.

Journal Article↗
PubMed1999

Linear stability analysis of walking vector solitons.

The linear stability analysis of two-parameter families of walking vector solitons of coupled nonlinear Schrödinger equations is performed. It is shown that the eigenvalues of the corresponding linearized problem can be complex valued in certain regions of the parameter space. The complex nature of the associated Lyapunov eigenvalues leads to a quite complicated pattern of instability regions of lowest-order soliton types. This pattern includes two typical situations: (i) the relevant eigenmode has a purely imaginary eigenvalue that passes through zero at the critical point and then becomes purely real, and (ii) the interplay between two discrete eigenmodes having purely imaginary eigenvalues leads to a bifurcation scenario where two imaginary eigenvalues merge together and become complex at the bifurcation point. It is shown that all known, lowest-order soliton types, namely slow, fast, in-phase vector, and out-of-phase vector, are dynamically stable in certain regions of the parameter space.

Journal Article↗
PubMed1993

Vitamin D3, a possible nuclear protector in normal hepatic and medullar tissue in white Wistar rats treated with cytostatics. Radioisotopic and cytogenetic aspects.

Vitamin D3 was given to male Wistar rats in 3 doses totalling 10,000 IU/kg b.w. then, within 24 hrs, girostan (10 mg/kg b.w.), lomustin or CCNU (10 mg/kg b.w.), all cytostatic substances, were injected in a single dose. Association of vitamin D3 with these cytostatics was found to reduce incorporation of 3H thymidine and a return to normal of RNA synthesis. This suggests that vitamin D3 has a protective effect by maintaining the stability of the double helix. Cytogenetically, the level of the recombinations and of the lesions themselves changes in relation to the structure of the alkylant used, and the damage is smaller if vitamin D3 is given before cytostatics.

Animals↗
PubMed1993

Chemical carcinogenesis as a factor altering the tissue ability to bind hormones. Benzo(a)pyrene--insulin interrelationship.

The present study was carried out on the uptake of 125I-insulin in the tissues or organs (liver, subcutaneous adipose tissue, striated muscle, renal cortex, frontal lobes of the brain) of normal Wistar rats or from animals treated with benzo(a)pyrene, a powerful carcinogen which s metabolically activated in the liver. The carcinogen was administered as follows: (a) in adult life by a single injected dose; (b) in early fetal life by administration to pregnant females and (c) in late fetal life, likewise by administration to the mothers. The results of combined administrations were studied as well. The ability of normal tissues to take up insulin was determined. The administration of a single benzo(a)pyrene dose produced marked alterations in binding of the hormone in some of the tissues, which might be attributed to certain general changes in the properties of the cell membranes. It has to be underlined that after the contact with the carcinogen in fetal life, the tissular ability to take up insulin is irreversibly and non-uniformly altered. This ability is easily influenced by a new carcinogenic dose.

Animals↗
PubMedDate not supplied

[The clinico-evolutionary considerations of 492 cases of measles hospitalized in the Infectious Disease Clinic Iaşi in 1997].

Between 01.01.1997-31.12.1997 in the Infections Diseases Clinical Hospital of Iaşi were admitted 492 patients suffering from measles. The above mentioned number of patients represents 4.92% of all the patients (10097) who were admitted during this period of time. More than half of the patients (56.9%) are residents in suburban arias. Teen-agers and young adults (15-24 years) were involved in most of the cases, followed by new born babies (0-11 months). The clinical signs were prevalent minor and the atypical exanthema was found in 1/4 of all cases. The most frequent complications were pneumonia, bronchopneumonia and otitis media. Of all the patients, two children (average age 1-4 years) died.

Adolescent↗
PubMedDate not supplied

[The clinical picture, treatment and prognosis of meningitis due to anaerobic and nonfermentative bacteria].

OBJECTIVES: The study of incidence, clinical manifestations and prognosis of meningitis with anaerobic and non-fermentative bacteria. MATERIAL AND METHOD: Retrospective study of 10 patients with severe forms of purulent meningitis admitted in the Hospital of Infectious Diseases of Iaşi, during 1.01.1990-31.12.1998. RESULTS: 3 of them were diagnosed with etiology with polymicrobial flora and the rest had etiology with: Peptostreptococcus (2 cases), Acinetobacter calcoaceticus (4 cases), Eikenella corrodens (1 case). The majority were male sex (8 cases), and from rural area (9 cases). The age of patients ranged from 2.5 to 59 years (the majority being adults of group of age 50-60 years). The gate of entrance was: iatrogenic in the majority of cases (6 cases), posttraumatic (2 cases) and othogen (2 cases); 3 cases being with cerebrospinal fluid fistula and 8 patients being in coma. The factors associated with poor prognosis were: the immunosuppression (chronic etilism--4 cases; bronchopneumonia--2 cases, pulmonary cancer--1 case) and the presence of the focal neurological findings on the noser of illness. The diagnosis was established by clinical characters and confirmed by isolating germs from cerebrospinal fluid. The treatment was done at the beginning with first intervention antibiotic association with a high spectrum and then according to the antibiogramme. The evolution was severe even under treatment with 3 deaths, the mortality being of 30.0%. CONCLUSIONS: We wished to present these cases as a general remark on the severity of illness, generally appeared on a suppressed ground, together with the rarity of those germs implicated in the etiology of purulent meningitis.

Acute Disease↗
PubMedDate not supplied

[Nosocomial staphylococcal meningitis].

OBJECTIVE: Clinical, bacteriological and therapeutically study on iatrogenic staphylococcal meningitis. METHOD: Retrospective analysis of 33 cases of iatrogenic staphylococcal meningitis admitted to the Hospital of Infectious Diseases of Iaşi in the interval 1988-1997. RESULTS: In the interval under study the recorded incidence was 1-5 cases per year. The predisposing factors were neurosurgical procedures for endocranial processes (12 cases), operated chronic otomastoiditis (11 cases), ventriculoatrial or peritoneal shunt (5 cases) and neurosurgical assessment (5 cases). The onset was slow, with persisting and mild headache persistence recurrence of fever, vomiting and convulsions followed by meningeal contracture and encephalitic phenomena. In 24 patients cerebrospinal fluid was typical for purulent meningitis. The causal agents were isolated in 25 cases being Staphylococcus aureus (20 cases) and Staphylococcus epidermidis sensitive to usual antistaphylococcal agents. Three therapeutically schemes were used the association cefotaxim î gentamycin proving to be the most effective vancomycin was required in but 2 cases. Three deaths were recorded. CONCLUSIONS: The symptoms of iatrogenic staphylococcal meningitis are mild marked by the underlying disease the most effective treatment being the association of cefotaxim with an aminoglycoside.

Adolescent↗
PubMedDate not supplied

[Neurologic manifestation in mumps virus infection].

OBJECTIVE: To study the incidence, clinical manifestations and treatment of mumps virus meningitis. MATERIAL AND METHOD: Study of 64 patients with mumps virus meningitis, admitted to the Clinic of Infectious Diseases of Iaşi during 1996-1999. RESULTS: The mumps virus meningitis had a high prevalence în 1998 (39%) most patients being males (62.5%) from the urban areas. 39.06% of cases were on the age group of 5-6 years old, 25% were in the age group 10-14 years old and 18.75% were adults patients. The clinical manifestation were dominated by headache (100%), fever (100%), vomiting (89%), photophobia (43.75%) and meningeal syndrome of contracture. The laboratory diagnosis was established by the cerebro-spinal fluid exam, together with the peripheric blood exam. The treatment was in all the cases with pathogenic (corticotherapy) and symptomatics with a very good evolution. CONCLUSIONS: All the cases with diagnosis mumps virus meningitis were well going, having good evolution and complete healing under symptomatic and pathogenic therapy.

Adolescent↗