Low power consumption integrated acousto-optic filter in domain inverted LiNbO3 superlattice

We report on an integrated acousto-optic filter in domain inverted LiNbO3 using a coplanar electrode configuration, which can achieve complete optical switching at electrical powers as low as 50 mW. These values are more than one order of magnitude lower than previously reported results [Opt. Lett. 34, 3205 (2009)]. In order to design the low power consumption devices, we have calculated surface acoustic wave excitation, propagation and acousto-optic interaction in the domain inverted LiNbO3 superlattice using scalar approximation and FEM analysis. Results from both modeling techniques are in good agreement with the experiments, including direct measurement of the acoustic displacement using laser interferometry and acousto-optic performance.

Integrated acousto-optic polarization converter in a ZX-cut LiNbO(3) waveguide superlattice

We report an integrated acousto-optic polarization converter exploiting a novel surface acoustic superlattice (S-ASL) transducer. The S-ASL transducer is made of a ZX-cut periodically poled lithium niobate (PPLN) crystal with uniform coplanar electrodes for surface acoustic wave (SAW) generation. For a PPLN period of 20 microm the SAW is excited at an rf of about 190 MHz, while the phase matching occurs at an optical wavelength of around 1456 nm. The measured mode conversion efficiency of 90% at an input rf power of 1 W and the 3 dB optical bandwidth of 2.5 nm confirm the confinement of the SAW between the electrode gap and the constructive interaction along the whole 10 mm electrode length.

Fiber strain sensor based on a pi-phase-shifted Bragg grating and the Pound-Drever-Hall technique

A fiber strain sensor based on a p-phase-shifted Bragg grating and an extended cavity diode laser is proposed. Locking the laser frequency to grating resonance by the Pound-Drever-Hall technique results in a strain power spectral density S(epsilon) (f) = (3 x 10(-19) f(-1) +2.6 x 10(-23)) epsilon(2)/Hz in the Fourier frequency range from 1 kHz to 10 MHz (epsilon being the applied strain), corresponding to a minimum sensitivity of 5 pepsilon Hz(-1/2) for frequencies larger than 100 kHz.

Very low voltage single drive domain inverted LiNbO(3) integrated electro-optic modulator

Domain inversion is used in a simple fashion to improve significantly the performance of a waveguide electro-optic modulator in z-cut LiNbO(3). The waveguide arms of the Mach-Zehnder interferometer are placed in opposite domain-oriented regions under the same, narrower and more efficient electrode, so that opposite phase shifts (push-pull effect) can still be achieved despite the arms being subjected to the same electric field. Switching voltages close to 2 V are obtained, which allow 10Gb/s modulation with inexpensive drivers, such as those used for electro-absorption modulators, which deliver driving voltages well below 3V.

Slow light in periodic superstructure Bragg gratings

A theoretical and experimental analysis of group velocity reduction in periodic superstructure Bragg gratings is presented. Experimental demonstration of group velocity reduction of sub-nanosecond pulses at the wavelength of optical communications is reported using a Moiré fiber grating.

Beam dynamics and wave packet splitting in a periodically curved optical waveguide: multimode effects

A theoretical and experimental analysis of beam dynamics and wave packet splitting of light in a periodically bent optical waveguide, a phenomenon recently observed [Phys. Rev. Lett. 94, 073002 (2005)] which is the optical equivalent of adiabatic stabilization of atoms in intense and high-frequency laser fields, is presented in the multimode operational regime. Inhibition of wave packet splitting is theoretically predicted and experimentally observed for higher-order mode excitation.

Observation of wave packet dichotomy and adiabatic stabilization in an optical waveguide

We report on the first experimental observation of wave packet dichotomy and adiabatic stabilization of light in a periodically bent optical waveguide in analogy with similar behavior of atoms in high-frequency strong laser fields.

Ray and wave instabilities in twisted graded-index optical fibers

We study ray and wave propagation in an elliptical graded-index optical fiber or lens with a twisted axis and show analytically the existence of an instability for both ray trajectories and beam moments in a finite range of axis twist rate embedded within the spatial frequencies of periodically focused rays for the untwisted fiber. By considering the paraxial ray equations and the paraxial wave dynamics in a rotating frame that follows the fiber axis twist, we reduce the dynamical problem of ray trajectories to the classical Blackburn's pendulum, which shows a dynamical instability, corresponding to classical diverging trajectories, due to the competing effects of confining potential, Coriolis force, and centrifugal force. A closed set of linear evolution equations for generalized beam moments are also derived from the paraxial wave equation in the rotating reference frame, revealing the existence of a dynamical moment instability in addition to the trajectory instability. A detailed analysis of beam propagation is presented in case of a Gaussian beam, and different dynamical regimes are discussed.

Familial juvenile autoimmune hypothyroidism, pituitary enlargement, obesity, and insulin resistance

The proband, a 9-year-old Hispanic female, presented with hair loss, strabismus, and weight gain. On magnetic resonance imaging (MRI) she was found to have severe primary hypothyroidism and a large pituitary mass. In addition, acanthosis nigricans, obesity, and hyperinsulinism were observed. Findings were similar in three of four siblings. Thyroid peroxidase antibodies were detected in the father and three of four siblings. Although all family members were obese, and hyperinsulinemia with high proinsulin and C-peptide was found in all except one sibling, only the mother and one child had overt type 2 diabetes mellitus. Because of the unusual association of autoimmune thyroid disease, insulin resistance and obesity rather than insulin deficiency, we searched for possible genetic abnormalities. The HLA haplotypes did not cosegregate with autoimmune thyroid disease or insulin resistance. Mutational analysis of known obesity genes was done. Leptin was not deficient, and sequencing of the proband's DNA showed no mutations in the perixisome proliferator activated receptor (PPAR)-gamma, PPAR-gamma(2), PPAR-alpha or melanocortin 4 receptor genes. Maternally inherited diabetes and deafness was ruled out since no mutations were found in mitochondria DNA. Insulin receptor antibodies were not detected. In conclusion, the remarkably high incidence of childhood autoimmune hypothyroidism, pituitary enlargement, insulin resistance and obesity in this family is not linked to known HLA types or known gene defects.

Amebic encephalitis caused by Balamuthia mandrillaris: report of four cases

We report four fatal cases of amebic encephalitis in children caused by the free-living pathogenic ameba Balamuthia mandrillaris. The clinical course ranged from subacute to fulminant. Provisional diagnoses were made either shortly before death or postmortem by an indirect immunofluorescent antibody test. Although the four cases occurred in different geographic locations, their common features may have diagnostic value for recognizing future cases of amebic encephalitis. The cases occurred in children 2 to 7.5 years old who were ostensibly immunocompetent and of Hispanic ethnicity. Three of the four children developed hydrocephalus during their illness. Increased awareness and timely diagnosis of this disease entity might lead to earlier intervention with improved outcome.

Quantum-mechanical analogy of beam propagation in waveguides with a bent axis: dynamic-mode stabilization and radiation-loss suppression

Wave propagation in an optical waveguide with a bent axis is studied under the scalar and paraxial wave approximations, and the quantum mechanical analogy with the electron dynamics in an atomic potential interacting with an intense electromagnetic field is highlighted. In particular we show that for a truncated parabolic waveguide with a periodically curved axis, a dynamic mode splitting with reduced radiation losses can be observed, which is fully analogous to the phenomenon of wave packet dichotomy and ionization quenching found in strong-field atomic physics.

Infected cardiac myxoma

Infected cardiac myxoma is a rare condition with variable presentation. We report a case of infected cardiac myxoma which presented as fever of unknown origin. Diagnostic considerations and treatment of this condition are discussed.

Brucellosis: unusual presentations in two adolescent boys

Two boys presented with variable signs and symptoms of infectious disease that challenged diagnosis. One of the two patients had aortic valve vegetations and lower extremity aneurysms, and the other had calvarial osteomyelitis, epidural abscess, pleural effusions, and pulmonary nodules. Only after a battery of bacterial and fungal agglutination tests was the unsuspected diagnosis made in each of brucellosis from Brucella canis.

Efficacy and safety of ampicillin/sulbactam and cefuroxime in the treatment of serious skin and skin structure infections in pediatric patients. UNASYN Pediatric Study Group

BACKGROUND

Pediatric skin and skin structure infections are often polymicrobial and require empiric therapy effective against pathogens that may be resistant to many antimicrobial agents. The present study tested the efficacy and safety of a parenteral beta-lactam/beta-lactamase inhibitor combination, ampicillin/sulbactam, and a beta-lactamase-stable cephalosporin, cefuroxime, in serious pediatric skin and skin structure infections requiring hospitalization and parenteral antimicrobial therapy.

METHODS

This was a multicenter, randomized, prospective, comparative open label trial that enrolled patients 3 months through 11 years of age. Patients received 150 to 300 mg/kg/day ampicillin/sulbactam in equally divided intravenous doses every 6 h. Cefuroxime was given in a dosage of 50 to 100 mg/kg/day either intravenously or intramuscularly in equally divided doses every 6 or 8 h. Maximum treatment was not to exceed 14 days. Patients could receive subsequent oral antimicrobial treatment at the investigator's discretion.

RESULTS

At final evaluation for clinical efficacy, 78.0% (n = 46) of the 59 evaluable patients who received ampicillin/sulbactam were cured and 22.0% (n = 13) were improved. The respective values for the 39 evaluable patients treated with cefuroxime were 76.9% (n = 30) and 23.1% (n = 9). At the end of treatment all pathogens were eradicated from 93.2% (n = 55) of 59 patients treated with ampicillin/sulbactam and from 100% of 39 who received cefuroxime. There were no significant differences between treatments in clinical or bacteriologic efficacy. Both ampicillin/sulbactam and cefuroxime were well-tolerated.

CONCLUSION

Both ampicillin/sulbactam and cefuroxime provide safe and effective parenteral antibiotic therapy in pediatric patients with serious skin and skin structure infections.

Pneumocystis carinii pneumonia in infants after heart transplantation

Although the reported incidence of Pneumocystis carinii pneumonia after heart transplantation in adults ranges from 3% to 40%, data are lacking regarding the incidence in the pediatric heart transplantation population. A retrospective review was performed on 152 infants (0 to 12 months of age) undergoing transplantation from November 1985 through December 1993 who survived at least 6 months after heart transplantation. Patients did not receive postoperative Pneumocystis carinii prophylaxis. Ten episodes (7%) were diagnosed in four neonates and six infants. The mean postoperative time to Pneumocystis carinii diagnosis was 5 months (range 3 to 9 months). Features of Pneumocystis carinii included hypoxia and tachypnea (10 of 10), progressive interstitial infiltrates (8 of 10), and persistent right middle lobe consolidation (1 of 10). Pneumocystis carinii was diagnosed with the use of bronchoscopy in eight cases and by open lung biopsy in two cases. Mean CD4 count available on five patients at the time of Pneumocystis carinii diagnosis was 413/mm3 (range 158 to 1358); 5 of 37 patients receiving antithymocyte induction had Pneumocystis carinii versus 5 of 115 patients who did not receive induction (p = 0.05). Patients were at increased risk for the development of Pneumocystis carinii if they had more than two episodes of rejection during the first year after heart transplantation (p = 0.04). All cases were successfully treated with trimethoprim/sulfamethoxazole. The incidence of Pneumocystis carinii in infant heart transplantation recipients is approximately 7% and appears most frequently in the first 6 months after the operation. Increased risk for Pneumocystis carinii may be related to early antithymocyte induction and increased episodes of rejection.

Emergency department presentation and management of pediatric heart transplant recipients

The object of this study was to review and delineate the presenting complaints, signs, symptoms, and Emergency Department (ED) management of pediatric heart transplant recipients who presented to Loma Linda University Medical Center's (LLUMC) Emergency Department. A retrospective chart review was made of all of the pediatric heart transplant patients who presented to the ED at LLUMC from January 1986 through February 1993. The department is part of a 600-bed university hospital with an associated 250-bed children's hospital that includes a pediatric heart transplant center and an ED that sees over 38,000 patients per year. The retrospective review collected information relating to chief complaint, physical findings, laboratory analysis, and diagnoses. Forty-seven patients (23%) presented to the ED for a total of 76 visits. The patients presented a median of 278 days (range 19 days to 6.5 years) after transplantation. The most common chief complaints were related to the respiratory tract, and the most common diagnoses (55%) were related to infectious processes. Fever was present in 21% of the visits. Three of 13 blood cultures obtained were positive. Cardiac symptoms were present in 14% of the visits with two rejection episodes. Hospital admission was required for 22 (29%) of the ED visits. Results showed that pediatric heart transplant recipients are most likely to present to the ED with infections. Although infections from opportunistic organisms and bacteremia must be considered, most infections are similar to those in the nontransplanted child. Life-threatening conditions such as graft rejection are less likely. Nevertheless, the emergency physician should maintain caution in the evaluation of these patients. Close cooperation and consultation with the transplant team will assure the optimal outcome for these patients.

Methotrexate therapy for complex graft rejection in pediatric heart transplant recipients. The Pediatric Heart Transplant Team--Loma Linda

BACKGROUND

We retrospectively reviewed all pediatric heart transplant recipients at Loma Linda University Medical Center between January 1990 and September 1993 to evaluate the efficacy and safety of methotrexate when it is used for the treatment of graft rejection.

METHODS

Twenty-eight of 156 patients (18%) received methotrexate therapy. The dose used for recurrent rejection was 10 mg/m2/week given every 12 hours for three doses. Rejection history, complete blood counts, liver function tests, and infectious complications were reviewed.

RESULTS

Eighteen patients were treated for recurrent rejection. Methotrexate was begun at a median of 115 days (13 to 1093 days). Older patients were more likely to receive methotrexate (p < 0.01). Efficacy was assessed as rejection episodes (mean +/- standard deviation) occurring in the 2 months before methotrexate administration compared with the 2 months after methotrexate administration and fell from 2.0 +/- 0.2 to 0.6 +/- 0.2 episodes (p < 0.001). The rejection rate (rejections per patient-month) fell in treated patients to a rate similar to patients who did not receive methotrexate. Two patients (11%) died while receiving methotrexate. An additional nine patients were treated for acute rejection with hemodynamic compromise, and one was treated for graft-versus-host disease. The incidence of significant infections was 50% (but no deaths were due to infection) during methotrexate therapy in all patients treated (n = 28). The minimum white blood cell count in the first month of methotrexate therapy occurred at 2 weeks (median of 2700 to 3500 x 10(6) cells/L). Only one patient had elevated transaminase levels.

CONCLUSION

Methotrexate is an effective and safe adjunct in the management of chronic pediatric cardiac graft rejection.

Concentrations of procaine and aqueous penicillin in the cerebrospinal fluid of infants treated for congenital syphilis

Penicillin concentrations in cerebrospinal fluid (CSF) were measured at various hours and days of treatment in 163 infants undergoing therapy for congenital syphilis. The CSF levels were compared for three treatment regimens. Aqueous penicillin G (A-PEN), 100,000 U/kg per day, was used in 23 infant, and a dosage of 200,000 U/kg per day was used in 40 patients; procaine penicillin G (P-PEN), 50,000 U/kg per day, was used in 100 children. Mean CSF penicillin levels were 0.416, 0.493, and 0.077 microgram/ml, respectively, in the three treatment groups. The mean CSF penicillin concentration among the 63 infants treated with either of the A-PEN regimens (0.465 microgram/ml) was significantly greater than the mean concentration (0.077 microgram/ml) among those treated with P-PEN (p < 0.001). Among those who received A-PEN, the difference in dosage was not associated with a significant difference in mean CSF penicillin concentration (p = 0.68). All the specimens obtained from patients who received A-PEN, but only 82% of those from patients who received P-PEN, had treponemicidal concentrations (> or = 0.018 microgram/ml). However, 33.3% (9/27) of specimens from infants who received P-PEN, tested between 18 and 24 hours after a dose, had CSF penicillin concentrations < 0.018 microgram/ml. These data suggest that administration of A-PEN may be the preferred therapy if CSF levels > 0.018 microgram/ml are desired, especially for infants with severe disease or congenital neurosyphilis.

Severe pneumonia after heart transplantation as a result of human parvovirus B19

The diverse manifestations of human parvovirus B19 infection have been well established. Erythema infectiosum, fetal hydrops, adult arthropathy, and aplastic anemia in patients with hemoglobinopathies or underlying immunocompromise have been described. Recently we successfully treated a patient who, after heart transplantation, had fever, rash, and pneumonia with respiratory failure caused by human parovirus B19. Human parovirus B19 has not been reported previously as a pathogen causing pulmonary disease after pediatric heart transplantation, and we wish to report it at this time.

Pediatric streptococcal toxic shock syndrome

Two children who presented with fever, rash, and hypotension were found to have group A beta hemolytic streptococcal toxic shock syndrome. These cases are reported to remind physicians who care for acutely ill children that exotoxin-producing streptococci can produce clinical features and multisystem failure similar to staphylococcal toxic shock syndrome.

Reliability of polymerase chain reaction in the detection of human immunodeficiency virus infection in children

During a 3-year period we followed 128 human immunodeficiency virus (HIV) antibody-positive children ages 6 days to 11 years clinically and with an HIV diagnostic panel consisting of antibody (by enzyme-linked immunosorbent assay and confirmed by indirect fluorescence assay or Western blot), p24 antigen detection, HIV isolation from peripheral blood culture and molecular detection of HIV nucleic acids by polymerase chain reaction (PCR). The PCR procedure included 30 cycles of amplification using two separate gag primer pairs (SK38/39 and SK101/145), followed by detection with probes to areas amplified (SK19 and SK102). Results of PCR were available within 48 hours and were sensitive (97%) and specific (100%). PCR should be obtained on all children exposed perinatally, and aggressive management should be undertaken for those found to be positive.