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At least 1,495 records · Page 83Linked to original sources
PubMed2006

Fabry-Perot optical binary switch for aircraft applications.

An optical binary switch for aircraft applications is demonstrated. A fiber Fabry-Perot interferometer (FFPI) bonded to a cantilever is used as the sensing element. A white-light interferometry system with two bulk Michelson interferometers sharing the same motor-driven translation stage is utilized to monitor the elongation of the FFPI. The system exhibits excellent linearity as a force sensor; the experimental results are in good agreement with theoretical calculated values. With a properly set threshold value, the system produces a binary output.

Journal Article↗
PubMed2006

Frequency-comb-referenced two-wavelength source for absolute distance measurement.

We propose a new tunable laser source concept for multiple-wavelength interferometry, offering an unprecedented large choice of synthetic wavelengths with a relative uncertainty better than 10(-11) in vacuum. Two lasers are frequency stabilized over a wide range of frequency intervals defined by the frequency comb generated by a mode-locked fiber laser. In addition, we present experimental results demonstrating the generation of a 90 mum synthetic wavelength calibrated with an accuracy better than 0.2 parts in 10(6). With this synthetic wavelength we can resolve one optical wavelength, which opens the way to absolute distance measurement with nanometer accuracy.

Journal Article↗
PubMed2006

Distributed measurement of birefringence dispersion in polarization-maintaining fibers.

A new method to measure the birefringence dispersion in high-birefringence polarization-maintaining fibers is presented using white-light interferometry. By analyzing broadening of low-coherence interferograms obtained in a scanning Michelson interferometer, the birefringence dispersion and its variation along different fiber sections are acquired with high sensitivity and accuracy. Birefringence dispersions of two PANDA fibers at their operation wavelength are measured to be 0.011 ps/(km nm) and 0.018 ps/(km nm), respectively. Distributed measurement capability of the method is also verified experimentally.

Journal Article↗
PubMed2026

Direct interaction between RSV polymerase L and active Rab11a mediates viral ribonucleoprotein transport to assembly sites.

Respiratory syncytial virus (RSV) is an enveloped, negative-sense, single-stranded RNA virus whose ribonucleoproteins (vRNPs) must be transported from cytoplasmic viral factories to the plasma membrane for efficient virion assembly. Viral vRNPs comprise genomic RNA encapsidated by nucleoprotein N and associated with the polymerase complex (L, P, and M2-1). It was previously demonstrated that newly synthesized vRNPs are transported along microtubules by hijacking Rab11a, a small GTPase involved in the regulation of recycling endosomes. In our previous study, we showed an interaction between Rab11a and vRNPs in infected cells by immunoprecipitation assays, nevertheless the molecular mechanisms underlying Rab11a viral hijacking remained unknown. Here, we provide the first comprehensive characterization of the interaction between RSV vRNPs and Rab11a using immunoprecipitation, immunofluorescence colocalization, GST pull-down assays, and biolayer interferometry. We demonstrate that the viral polymerase L is the sole vRNPs component responsible for Rab11a recognition: immunoprecipitation of L specifically co-precipitates HA-tagged Rab11a, whereas other vRNPs proteins show no interaction. In vitro binding studies confirm that L interacts directly and specifically with the active, GTP-bound form of Rab11a with sub-micromolar affinity. Domain mapping using truncated constructs reveals that this interaction requires the C-terminal methyltransferase and CTD domains of L (residues 1756-2165) and depends on Rab11a's Switch I region, known to mediate interactions with cellular Rab11a partners. Mutagenesis further highlights leucine 1860 in the L polymerase as critical for Rab11a binding. Competitive inhibition of the interaction between Rab11a and L using the minimal Rab11a-binding domain significantly impairs vRNP dynamics during infection, indicating that Rab11a-L binding is involved in the transport of vRNPs. Together, these findings establish RSV polymerase L as the key mediator of Rab11a engagement, define the molecular interface of their interaction, and reveal a potentially conserved viral strategy for genome transport. Targeting the L-Rab11a interaction could therefore be a promising strategy for the development of RSV-specific or broad-spectrum antiviral therapies.

rab GTP-Binding Proteins↗
PubMed2004

Organ of Corti potentials and the motion of the basilar membrane.

During sound stimulation, receptor potentials are generated within the sensory hair cells of the cochlea. Prevailing theory states that outer hair cells use the potential-sensitive motor protein prestin to convert receptor potentials into fast alterations of cellular length or stiffness that boost hearing sensitivity almost 1000-fold. However, receptor potentials are attenuated by the filter formed by the capacitance and resistance of the membrane of the cell. This attenuation would limit cellular motility at high stimulus frequencies, rendering the above scheme ineffective. Therefore, Dallos and Evans (1995a) proposed that extracellular potential changes within the organ of Corti could drive cellular motor proteins. These extracellular potentials are not filtered by the membrane. To test this theory, both electric potentials inside the organ of Corti and basilar membrane vibration were measured in response to acoustic stimulation. Vibrations were measured at sites very close to those interrogated by the recording electrode using laser interferometry. Close comparison of the measured electrical and mechanical tuning curves and time waveforms and their phase relationships revealed that those extracellular potentials indeed could drive outer hair cell motors. However, to achieve the sharp frequency tuning that characterizes the basilar membrane, additional mechanical processing must occur inside the organ of Corti.

Acoustic Stimulation↗
PubMed2004

Dynamics of the DNA duplex formation studied by single molecule force measurements.

DNA is partly denatured in vitro by applying a force that mechanically separates the two strands of the double helix. Sudden reduction of the imposed displacement triggers spontaneous reannealing of the molecule. The corresponding force signals are measured by optical trapping interferometry for backward steps of various amplitudes and base sequence intervals. The measured signals frequently show plateaus of varying duration at discrete values that are dependent on the base sequence. Additional measurements are performed with proteins bound to the double helix. When the opening fork encounters such a protein during mechanical unzipping, force increases until the protein is ejected. This ejection induces fast release of tension and fast unzipping. Comparing our different measurements, we find that both DNA unzipping and the relaxation of tension in DNA are faster than the formation of the double helix.

Computer Simulation↗
PubMed2005

Mechanical responses of the organ of corti to acoustic and electrical stimulation in vitro.

The detection of sound by the cochlea involves a complex mechanical interplay among components of the cochlear partition. An in vitro preparation of the second turn of the jird's cochlea provides an opportunity to measure cochlear responses with subcellular resolution under controlled mechanical, ionic, and electrical conditions that simulate those encountered in vivo. Using photodiode micrometry, laser interferometry, and stroboscopic video microscopy, we have assessed the mechanical responses of the cochlear partition to acoustic and electrical stimuli near the preparation's characteristic frequency. Upon acoustic stimulation, the partition responds principally as a rigid plate pivoting around its insertion along the spiral lamina. The radial motion at the reticular lamina greatly surpasses that of the tectorial membrane, giving rise to shear that deflects the mechanosensitive hair bundles. Electrically evoked mechanical responses are qualitatively dissimilar from their acoustically evoked counterparts and suggest the recruitment of both hair-bundle- and soma-based electromechanical transduction processes. Finally, we observe significant changes in the stiffness of the cochlear partition upon tip-link destruction and tectorial-membrane removal, suggesting that these structures contribute considerably to the system's mechanical impedance and that hair-bundle-based forces can drive active motion of the cochlear partition.

Acoustic Stimulation↗
PubMed2005

Comparison of polyethylene wear associated with cobalt-chromium and zirconia heads after total hip replacement. A prospective, randomized study.

BACKGROUND: A ceramic femoral head is an alternative to a metal femoral head for the bearing surface of total hip arthroplasty. The purpose of this study was to compare polyethylene wear in patients who had undergone bilateral total hip arthroplasty with implants that differed only with regard to the material used for the femoral head: a zirconia head was used on one side, and a cobalt-chromium head was inserted on the contralateral side. METHODS: A prospective, randomized study was performed to evaluate the outcomes in fifty-two patients who had undergone sequential bilateral primary total hip replacement. A zirconia head was used in one hip, and a cobalt-chromium head was used in the other. There were forty-eight men and four women; the mean age at the time of surgery was 44.2 years. The mean duration of follow-up was 7.1 years. Clinical and radiographic evaluations were performed preoperatively and at six weeks; three, six, and twelve months; and yearly postoperatively. Linear wear of the polyethylene liner was measured radiographically. Two femoral components with a zirconia head had aseptic loosening and were revised. The explanted heads were evaluated with use of interferometry, environmental scanning electron microscopy, and x-ray diffraction studies. RESULTS: The mean polyethylene wear rate was 0.08 mm/yr in association with the zirconia heads and 0.17 mm/yr in association with the cobalt-chromium heads (p = 0.004). The mean amount of volumetric polyethylene wear was 350.8 mm3 in association with the zirconia heads and 744.7 mm3 in association with the cobalt-chromium heads (p = 0.004). With regard to surface roughness, the Ra values of the two explanted zirconia heads were 15.87 and 17.35 nm and the Rpm values were 153.86 and 156.18 nm. Two identical zirconia heads that had not been implanted had Ra values of 5.31 and 5.48 nm and Rpm values of 65.27 and 66.35 nm. Four unimplanted cobalt-chromium heads that were identical to the ones implanted in this study had Ra values ranging between 25 and 50 nm and Rpm values ranging between 262.6 and 525.2 nm. Little phase transformation was noted in the two revised zirconia heads. CONCLUSIONS: The mean amount and rate of polyethylene wear were significantly lower in the hips with a zirconia head than they were in the hips with a cobalt-chromium head, presumably because the zirconia heads had a smoother articulating surface.

Adult↗
PubMedDate not supplied

Vibration measurement of the human tympanic membrane--in vivo.

The vibration patterns of the human eardrum in vivo have been recorded by time average electronic speckle pattern interferometry--ESPI. The necessary stability was achieved by shortening the exposure time of each TV frame. The amplitude--and phasedistribution was mapped across the drum by phase-modulation techniques which also could show the vibrations in slow motion. By photoelectric detection of the TV image intensity, amplitudes down to 2 nm could be measured. Preliminary results are presented.

Holography↗
PubMed1981

Evidence for orbital deformation that may contribute to monocular blindness following minor frontal head trauma.

Traction injury to the optic nerve and vasa nervorum is the suggested etiology for monocular blindness following trivial frontal trauma. Holographic interferometry was used on human skulls to demonstrate orbital deformation in response to nondestructive frontal loading. The findings suggest an additional mechanism for energy dissipation and therefore for optic nerve injury following frontal impact.

Blindness↗
PubMed1983

A study of human head vibrations using time-averaged holography.

Intact human cadaver heads were subjected to vibrations. The resonant frequencies over a range of 500 to 3000 Hz were determined. Vibration patterns at three frequencies were presented by means of time-averaged holography. The displacements were quantified and the highest amplitudes were found in the temporal region. Antinode centers were found superimposed on the squamatic suture. This method of holographic interferometry allows sensitive deformation measurements to be taken on intact human heads or skulls.

Cadaver↗
PubMedDate not supplied

Surface roughness in PMMA is linearly related to the amount of excimer laser ablation.

OBJECTIVE: To determine if surface roughness after excimer laser ablation is a function of the amount of ablation and to identify a standard unit for ablation roughness. METHODS: We used a VISX 20/20 excimer laser to perform a series of single zone 6-mm diameter ablations (photorefractive keratectomy [PRK]) in polymethylmethacrylate (PMMA). Corrections ranged from -1.00 diopter (D) to -15.00 D. A scanning white light interferometry microscope (Zygo Corp, Middlefield, Conn) was used to quantify the surface roughness at the center of each ablation. RESULTS: We found a linear increase in surface roughness as the refractive correction increased. Each diopter increment resulted in an approximately 300 nm increased peak-to-valley measurement. This represented an increase of 25 nm roughness per micron of ablation in PMMA. CONCLUSIONS: Surface irregularities in PMMA increase with ablation depth. We propose a unit of measure of roughness, the "ablation," expressed as the peak-to-valley distance in nm/divided by m of ablation.

Humans↗
PubMedDate not supplied

Corneal sensitivity and some properties of the tear film after laser in situ keratomileusis.

PURPOSE: To investigate central corneal sensitivity, lipid layer structure of the precorneal tear film, and tear volume after laser in situ keratomileusis (LASIK). METHODS: Central corneal sensitivity was measured using the Non-Contact Corneal Aesthesiometer. The aesthesiometer was mounted on a slit lamp and an airpulse of controlled pressure was directed onto the cornea. When central corneal sensitivity was reduced, a higher air pulse pressure was required to stimulate the cornea. The final central corneal sensitivity threshold measured was recorded in millibars. Tear lipid layer structure was assessed by optical interferometry and classified according to appearance using the Keeler Tearscope. Tear volume was measured using the phenol red cotton thread test. Subjects were recruited from a group of patients after LASIK who had experienced no complications (n=22). The average postoperative time was 14 weeks and measurements were taken on one eye. In bilateral cases, measurements were recorded from the right eye only. Average attempted correction was -6.30 D (range, -2 to -11 D). Age-matched controls were later recruited for central corneal sensitivity threshold (n=24). A second group of age-matched controls were recruited for tear volume and lipid layer structure (n=24). RESULTS: The median (range) was 1.1 mbars (0.2 to 4.3 mbars) after LASIK and 0.58 mbars (0.20 to 1.3 mbars) in the controls; the difference was statistically significant (P = .043). The lipid layer of the tear film tended to be thinner in eyes after LASIK compared with controls (P = .032). The mean (+/- SD) tear volume was 16.9 +/- 8.3 mm after LASIK and 19.8 +/- 7.1 mm in controls. This difference was not statistically significant (P = .492). CONCLUSION: At 14 weeks postoperatively, central corneal sensitivity was below normal levels and the tear lipid layer was thinner. The poorer quality lipid layer may predispose to symptoms of dry eye after LASIK.

Adolescent↗
PubMedDate not supplied

Smoothness of ablation on polymethylmethacrylate plates with four scanning excimer lasers.

PURPOSE: To perform a quantitative evaluation of smoothness of ablation on polymethylmethacrylate (PMMA) using four scanning excimer lasers available commercially for photorefractive surgery. METHODS: Ablations were done on PMMA plates with dimensions 100 x 50 x 1 mm. Four scanning excimer lasers were used, two with flying spot technology (Zeiss-Meditec MEL-70, and a Russian-made unit, Microscan) and two Nidek models with scanning slit delivery systems and an expanding iris diaphragm (EC-5000 and EC-5000 CX). Forty PMMA plates were ablated with standard -3.00-D settings using an ablation zone of 6 mm; each laser ablated 10 plates. Measurements were made in the center of each plate with the Zygo microscope, based on the principle of white light interferometry. Smoothness of ablation was characterized by three surface parameters (RMS, Ra, PV). RMS was considered the most significant parameter. RESULTS: The smoothest surface was obtained in samples produced by Zeiss-Meditec MEL-70 unit (RMS=112 +/- 23 nm), followed by the Nidek EC-5000 CX (RMS=153 +/- 12 nm), and the Microscan (RMS=181 +/- 11 nm). The smoothness of ablation produced by the Nidek EC-5000 unit (RMS=329 +/- 39 nm) was significantly less than the other three lasers (P<.01). CONCLUSIONS: Scanning excimer lasers based on flying spot technology--Zeiss-Meditec MEL-70 and Microscan, as well as the Nidek EC-5000 CX with FlexScan--created smoother ablations on PMMA plates compared to the older Nidek EC-5000 unit.

Cornea↗
PubMedDate not supplied

A test eye for wavefront eye refractors.

PURPOSE: A multi-site study was conducted to test feasibility of a modified automatic refractor style test eye as a test device for wavefront refractors of various types and to determine whether a) they could be measured and b) when measurements could be made, to see if they were similar. This study did not attempt to assess which instrument most accurately measures the aberrations of the test eye or human eye. METHODS: Three automatic refractor style test eyes were modified for use as test devices for wavefront refractors. One had a simple spherical front surface, and two had additional aberrations added. The test eyes and holder were circulated to 11 test sites where attempts were made to measure them with eight different wave-front refractor systems. RESULTS: Eight (100%) of the eight wavefront refractor systems tested successfully measured the test eyes. The systems did not give similar results for the same test eye. In some cases, coma was reported where none was present. Differences in reported defocus values reflect different approaches for compensating for the dispersion of the eye. A corneal topography system could measure and recognize the aberrations of the test eyes as well as the wavefront refractor systems tested. Interferometry, on the other hand, did not prove to be a successful method to assess the surface of the test eyes. CONCLUSIONS: The test eye design may be used as a test device for wavefront refractor systems. This type of test eye can detect systematic differences between various wavefront refractors and can serve as a useful calibration and comparison tool.

Diagnostic Techniques, Ophthalmological↗
PubMed1999

Photoproduct formation from a zinc benzochlorin iminium salt detected by fluorescence microscopy.

When examined by fluorescence microscopy, tumor cells loaded with a zinc benzochlorin iminium salt showed a very faint deep-red fluorescence that was rapidly transformed to a substantially brighter red-orange fluorescence. Fourier transfer spectroscopy analysis with a red-sensitive detection system revealed that an initial fluorescence at 770 nm was gradually converted to 640 nm fluorescence during excitation. Image analysis showed that photoproduct formation was accompanied by a change in the site of drug localization from the cytoplasm to the nucleus. These studies illustrate the power of interferometry for the characterization of photoproducts and changes in sensitizer localization during photoproduct formation.

Animals↗