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At least 595 records · Page 33Linked to original sources
PubMed1983

Prometaphase forces towards opposite spindle poles are not independent: an on/off control system is identified by ultraviolet microbeam irradiations.

Individual spindle fibres in prometaphase spermatocytes of the cricket, Neocurtilla hexadactyla, were irradiated with an ultraviolet microbeam. The stretched heteromorphic bivalent (X2Y) contracted to about 75% of its pre-irradiation length after irradiation of either of its two oppositely directed spindle fibres (i.e., the X2 or Y spindle fibre). The X2Y bivalent also contracted after irradiation of the connection between the kinetochores of the univalent X1 chromosome and the Y chromosome but it did not contract after irradiation of autosomal spindle fibres or of the spindle fibre of the X1 univalent sex chromosome. The spindles sometimes shrank after irradiation, but contraction of the X2Y bivalent was independent of spindle shrinkage. The data strongly suggest that the oppositely directed forces on a bivalent are not independent. One reason is that the X2Y contractions were asymmetrical: during contraction one kinetochore remained fixed in position while the other kinetochore (facing the opposite pole) moved towards the equator. In 75% of the cases the stationary kinetochore was associated with the irradiated spindle fibre. Thus, we suggest that the irradiation of a spindle fibre produces a state analogous to rigor in the irradiated spindle fibre and, because of effects on the control system, produces relaxation of tension in the oppositely directed non-irradiated spindle fibre, so that the kinetochore associated with the non-irradiated spindle fibre moves towards the equator. These experiments have identified a control system that coordinates force production to opposite poles.

Animals↗
PubMed1988

polo, a mitotic mutant of Drosophila displaying abnormal spindle poles.

Neuroblast cells in larvae homozygous for mutant alleles of the locus polo show a high frequency of metaphases in which the chromosomes have a circular arrangement, and anaphase figures in which chromosomes appear to be randomly oriented with respect to at least one of the spindle poles. These defects appear to lead to the production of polyploid cells. Sex chromosome disjunction is affected in male meiosis, primarily in the second division, and the meiotic spindles of living cells are abnormal. One allele is a larval lethal, whereas another is semi-lethal with about 7% of homozygotes surviving as adults. Embryos from homozygous polo females have aberrant mitotic spindles that are highly branched and have broad poles. Immunofluorescence studies with an antibody that recognizes an antigen associated with the centrosome indicate that the organization of this organelle is disrupted in the mutant embryos.

Animals↗
PubMed2006

Upper pole of a duplex kidney mimicking adrenal incidentaloma in 18F-fluoro-2-deoxy-D-glucose positron emission tomography: a pitfall in diagnosis.

18F-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) has proved to be valuable in the diagnosis and management of a variety of malignancies, but is still limited in providing detailed anatomical information. According to the literature, an adrenal incidentaloma with high FDG uptake usually indicates malignancy and requires further investigation. However, accurate localization of the adrenal gland in FDG-PET is difficult without the presence of surrounding well-visualized organs, such as the kidney or liver. If these organs have a congenital anomaly or are altered due to a previous operation, misdiagnosis can occur. We present a case with right partial duplex kidney accompanied by abnormal urine retention in the upper pole, which was misinterpreted as an adrenal incidentaloma in FDG-PET. A subsequent CT scan revealed a normal right adrenal gland, but a right partial duplex kidney. Fusion of the PET and CT images showed that the right adrenal lesion seen in the PET image corresponded to the upper pole of the duplex kidney.

Adrenal Gland Neoplasms↗
PubMed1999

Measuring the effects of street pole banners on consumer awareness and preference.

The authors used a relatively new advertising medium to increase public awareness of their children's hospital. They found that street pole banners, a form of outdoor advertising, made a measurable, positive impression on consumer consciousness. Banners effectively supplemented a product awareness campaign that included more traditional media. This study is the first documentation of the use of banners to market health care services. Using a two-phase approach, respondents were surveyed via telephone before and after exposure. Results of the follow-up survey show significant increases in levels of awareness and preference. The authors hope their report on the successful use of street pole banners will spur further research on the use of this innovative media.

Advertising↗
PubMed1985

Fragmentation of the proximal pole of the patella. Another manifestation of juvenile traction osteochondritis?

Six boys with fragmentation of the proximal pole of the patella are reported; the condition was bilateral in one. Four of the six presented with symptoms of Osgood-Schlatter's disease or Larsen-Johansson disease of the same or of the contralateral knee, but they had no symptoms or signs relating to the proximal pole of the patella; one also had features suggesting minimal chondromalacia patellae. Two boys had no objective abnormality in either knee. It is suggested that the fragmentation may be a further form of traction osteochondritis of the attachments of the quadriceps mechanism. Attention is drawn to its characteristic radiographic appearance, its association with other forms of juvenile traction osteochondritis (which are commonly symptomatic), and to its occurrence in boys aged 10 or 11 years.

Child↗
PubMed2003

Polarization control by use of the electro-optic effect in periodically poled lithium niobate.

We propose a method to control the polarization of light by the electro-optic effect in periodically poled lithium niobate. A single integrated chip of Z-cut lithium niobate having two sections is used. The first section is not periodically poled, whereas the second section is. With an electric field applied along the Z axis of the first section and another electric field applied along the Y axis of the second section, light with an arbitrary elliptical polarization can be converted into a fixed linearly polarized state.

Journal Article↗
PubMed2005

Broadening of the second-harmonic phase-matching bandwidth in type II periodically poled KTP.

We have theoretically demonstrated type II broadband second-harmonic generation (SHG) based on a quasi-phase-matching (QPM) configuration in periodically poled KTP (PPKTP). The wavelength dependence of QPM grating periods at different temperatures of 5 degrees C, 25 degrees C, and 45 degrees C is calculated with the crystal length of 1 cm. We find a very wide bandwidth, as large as 42.6 nm, of fundamental wavelength of 1.58 microm at the telecommunication band with the QPM period of 48.9 microm at 25 degrees C. The corresponding bandwidths of incident angle and temperature are found to be 4.24 degrees and 14.8 degrees C, respectively. The comparison among PPKTP, periodically poled lithium niobate (PPLN), and MgO:PPLN reveals the unique performance of PPKTP in the broadband SHG.

Journal Article↗
PubMed2005

Measurement of depletion region width in poled silica.

The width of the depletion region in fused-silica samples thermally poled during various periods of time is investigated experimentally with four previously reported characterization techniques in an attempt to unify their findings. Although all measurements give a similar width of the depletion region, it is shown that the determination of the profile of chi(2) is also required for a good estimate of the nonlinearity induced by poling.

Journal Article↗
PubMed2005

Investigation of multiconversion processes in periodically poled LiNbO3-based optical parametric oscillators.

The multiconversion processes in optical parametric oscillators based on periodically poled LiNbO3 are investigated. Interpretations based on simultaneous quasi- and birefringent phase matching are presented. Three parametric and three harmonic generation processes in a multigrating periodically poled LiNbO3 crystal were observed. Two of the parametric processes and two of the harmonics were quasi-phase matched, and the other conversion processes were phase matched through birefringence in the crystal. The primary parametric process (omegap --> omegas + omegai) was obtained through first-order quasi-phase matching. The other quasi-phase-matched processes occurred within higher orders. The existence of even-order quasi-phase matching in the crystal is due to other than a 50% duty-cycle grating periods. The tuning range for each of the generated waves is obtained and compared with theoretical fittings.

Journal Article↗
PubMed2006

Overcoming the impeding effect of core-cladding interface on the progression of the second-order nonlinearity in thermally poled optical fibers.

The spatial distribution of the second-order optical nonlinearity in thermally poled optical fibers was characterized with second-harmonic microscopy. The second-order optical nonlinearity (SON) was found to be distributed in a layer, the progression of which was impeded at the core-cladding interface, which acted as an extra potential barrier to the migrating ions. At higher poling voltages and temperatures, the SON layer could overcome this barrier and extend further into the fiber core. The polarization dependence of the optical nonlinearity within the fiber core was also checked and found to be almost negligible.

Journal Article↗
PubMed2003

Quadratic spatial solitons in periodically poled KTiOPO4.

The evolution of fundamental beams into quadratic spatial solitons was investigated in a periodically poled bulk KTiOPO4 crystal near and at phase matching. Various soliton properties, such as trapping efficiency as a function of phase mismatch, poling-induced walk-off, and the effects of pulse width, beam width, and input beam quality, were measured. Effects attributed to the presence of cubic nonlinearities were also observed.

Journal Article↗
PubMed2003

Poled polymer thin-film gratings studied with far-field optical diffraction and second-harmonic near-field microscopy.

Electrical poling induces polar ordering of molecules in a grating that has been holographically inscribed on a thin film of polymer with azobenzene side chains. The resulting chi2 grating, seen by second-harmonic-generation (SHG) near-field scanning optical microscopy, can have a periodic structure that is significantly different from the topographical image. The far-field linear and SHG diffration patterns correlate well with the grating structures. Poling of the thin-film grating, which presumably has photodriven nonuniform material properties within each period, leads to the more complex structure of the chi2 grating.

Journal Article↗
PubMed2003

Efficient 340-nm light generation by a ridge-type waveguide in a first-order periodically poled MgO:LiNbO3.

Quasi-phase-matched (QPM) UV second-harmonic generation (SHG) in a periodically poled MgO:LiNbO3 waveguide is presented. A ridge-type waveguide with high nonlinearity and strong resistance to photorefractive damage was achieved by use of an ultraprecision machining technique. By use of this waveguide in 1.4-microm periodically poled MgO:LiNbO3, a first-order QPM SHG device for 340-nm UV radiation was demonstrated. In a single-pass configuration, continuous-wave 22.4-mW UV light was generated for a fundamental power of 81 mW, corresponding to a normalized conversion efficiency of 340%/W.

Journal Article↗
PubMed2004

Room-temperature, continuous-wave 1-W green power by single-pass frequency doubling in a bulk periodically poled MgO:LiNbO3 crystal.

Continuous-wave high-power green light generation at room temperature is reported in a single-pass frequency-doubling configuration with bulk periodically poled MgO:LiNbO3 crystal placed outside a diode end-pumped Nd:GdVO4 laser. The MgO:LiNbO3 samples of 6.95-microm domain period, uniform periodicity, and 50% duty cycle along the entire crystal length are fabricated by use of a high-voltage multipulse poling method. A maximum power of 1.18 W at 531 nm with 16.8% conversion efficiency is obtained from a 2-mm-thick, 25-mm-long MgO:LiNbO3 crystal; the corresponding internal green power and conversion efficiency are 1.38 W and 19.6%, respectively, whereas the normalized conversion efficiency is 3.3%/W.

Journal Article↗
PubMed2004

400-photon-per-pulse ultrashort pulse autocorrelation measurement with aperiodically poled lithium niobate waveguides at 1.55 microm.

We demonstrate ultrasensitive intensity autocorrelation measurements of subpicosecond optical pulses in the telecommunication band by using aperiodically poled lithium niobate (A-PPLN) waveguides. The tightly confined optical beam in the waveguides and the chirped poling period facilitate simultaneous high second-harmonic generation (SHG) efficiency and broad phase-matching (PM) bandwidth. The resulting measurement sensitivity is 3.2 x 10(-7) mW2, approximately 500 times better than the previous record for intensity autocorrelations. We also show that chirped A-PPLN waveguides retain nearly the same SHG efficiency as the unchirped guide as long as the PM bandwidth is not significantly broader than the input spectrum.

Journal Article↗
PubMed2004

200-m optical fiber with an integrated electrode and its poling.

More than 200 m of germanosilica optical fiber is manufactured with an internal wire electrode running parallel to the core. In this new fabrication method the wire is integrated into the fiber during the draw process. This length of fiber is an order of magnitude longer than other previously reported fibers with internal electrodes. The optical loss is less than our measurement floor of 0.5 dB/m at 1550 nm. A 0.9-m section of the fiber is thermally poled, inducing a permanent second-order nonlinearity of 0.0125 pm/V. Methods to increase the induced nonlinearity are discussed. Integrating the wire into the fiber during the draw allows lengths of fiber with internal electrodes greater than 1 km to be manufactured and subsequently poled.

Journal Article↗
PubMed2005

Microstructure of a poled surface-relief grating and its electro-optic response.

The microstructure of a poled surface-relief grating of an azobenzene side-chain polymer film is investigated. From the in situ monitoring of diffraction efficiency and second-harmonic generation, as well as dynamic-contact electrostatic force microscopy images, the point group symmetry of C2nu is identified. The polarization-dependent electro-optic measurement of the reflected diffraction order further confirms the optically biaxial structure of the poled surface-relief grating.

Journal Article↗
PubMed2005

Generation of high-contrast millijoule pulses by optical parametric chirped-pulse amplification in periodically poled KTiOPO4.

A new high-contrast, high-gain optical parametric chirped-pulse amplifier (OPCPA) architecture is demonstrated in periodically poled KTiOPO4 (PPKTP). This architecture overcomes parametric fluorescence contrast limitations of the OPCPA in periodically poled materials. The scheme is based on two passes of a single relay-imaged pump pulse and a free-propagating signal pulse through a 1.5 mm x 5 mm x 7.5 mm PPKTP crystal. The output energy of 1.2 mJ is generated at a center wavelength of 1053 nm by 24 mJ of pump energy. A prepulse contrast level of > 3 x 10(7) was measured with > 10(6) saturated gain in the amplifier. Amplified pulses were compressed to 200 fs. This simple and versatile concept requires only a modest pump energy from a commercial pump laser and represents a possible high-contrast front end for high-energy Nd:glass-based petawatt-class lasers.

Journal Article↗