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At least 217 records · Page 12Linked to original sources
PubMed1994

Depth of field of plus lenses and reading telescopes.

Using simple optical equations we solved for the depth of field (or range of movement for clear viewing) of plus lenses and near telescopes of the same equivalent power and then compared them. The prevalent clinical wisdom states that reading telescopes have a smaller depth of field than plus lenses. Our results show depth of field to be equal for both and inversely proportional to the square of the equivalent power. A simple nomograph of depth of field vs. power has been prepared for clinicians to use.

Eyeglasses↗
PubMed2004

Localization and nonlinear resistance in telescopically extended nanotubes.

We have measured the electrical resistance R between the ends of a multiwall carbon nanotube during telescopic extension of the nanotube. R increases monotonically with extension and is hysteresis free, demonstrating that a telescoping nanotube constitutes a near-ideal nanometer-scale rheostat. The functional form of R is nonlinear and consistent with an exponential form predicted for a one-dimensional localized system, with a characteristic localization length 1000-1500 nm.

Journal Article↗
PubMed2002

The telescoping suture--Part II: A novel method to improve the mechanical behavior of a new biomaterial: ostrich pericardium.

Ostrich pericardium, sutured using a telescoping or overlapping technique, was studied to determine its mechanical behavior. From each of 12 pericardial sacs, four contiguous strips were cut longitudinally, from root to apex, and another four contiguous strips were cut in transverse direction. One of the strips in each set of four was used as an unsutured control and the remaining three were sutured by overlapping 0.5 cm of the tissue and sewing with Gore-tex, Prolene or Pronova. These 96 samples were then subjected to tensile testing along their major axes until rupture. The tensile stresses recorded in the suture materials at the moment tears appeared in the pericardium ranged between 55.99 MPa and 70.23 MPa for Gore-tex in samples cut in the two directions. Shear stress became ostensible at 56 MPa, with clearly evident tears. However, microfracture of the collagen fibers must be produced at much lower stress levels. The comparison of the resistance in kilograms (machine-imposed), without taking into account the sections in which the load was applied, demonstrated only a slight loss of load when the telescoping suture was employed in ostrich pericardium samples. Ostrich pericardium may continue to be an alternative biological material for the construction of heart valve leaflets.

Animals↗
PubMed2006

Implantation of left ventricular leads using a telescopic catheter system.

BACKGROUND: Implantation procedures for cardiac resynchronization therapy (CRT) remain challenging with regard to coronary sinus (CS) cannulation and left ventricular (LV) lead positioning. Technologic advances in catheter design may facilitate CS cannulation and LV lead placement. AIMS: To evaluate two different telescoping dual-catheter systems, RAPIDO Guiding Catheter System (Group R) and RAPIDO ADVANCE Guiding Catheter System (Group A) (Guidant Inc., St. Paul, MN, USA), during implantation of a CRT device. METHODS: Seventy-four consecutive patients randomly received a CRT device using the R or A system. RESULTS: An LV lead was successfully implanted in 74 patients (100%). (1) Median times for CS cannulation in groups R and A were 0.3 minutes (range from 0.05 to 14 minutes) and 0.5 minutes (range from 0.05 to 9 minutes), respectively (P = NS). (2) Median times for LV lead placement were 8 minutes (range from 0.8 to 100 minutes) and 3.5 minutes (range from 0.25 to 30 minutes), respectively, for groups R and A (P = 0.032). (3) Median total fluoroscopy times were 12.33 minutes (range from 5 to 70 minutes) and 14.33 minutes (range from 6 to 53 minutes) for groups R and A, respectively (P = NS). (4) Median procedural times for CRT implantation were 80 minutes (range from 40 to 200 minutes) and 75 minutes (range from 45 to 180 minutes) (P = NS) in groups R and A, respectively. There were no major complications. CONCLUSION: CS cannulation and LV lead placement with a telescopic dual-catheter system is a safe and feasible approach that may reduce fluoroscopy and overall CRT implantation times. Our observations suggest that the RAPIDO ADVANCE System is faster than the RAPIDO System in terms of median time for LV lead positioning.

Aged↗
PubMed2004

Mandibular two-implant telescopic overdentures.

To stabilize mandibular overdentures in edentulous patients, various connector types which can be attached to between two and four implants placed in the anterior mandible are possible. Treatment using non-rigid telescopic connectors on two interforaminal implants for overdenture stabilization began in 1989. The objective of this study is to investigate soft- and hard-tissue conditions as well as prosthesis function after a period of 10 years. This also involved an evaluation of correlations between radiographic and clinical parameters. Twenty-three subjects with 46 interforaminal implants (ITI solid screw implants, 12 mm in length, 4.1 mm in diameter; 10.4 years in situ, range, 8-12.8 years) were investigated. Modified plaque index (mPI), sulcus fluid flow rate (SFFR), modified sulcus bleeding index (mBI), probing depth (PD), distance from implant crown margin to the coronal border of the peri-implant mucosa (DIM), attachment level (AL), width of keratinized mucosa (KM), Periotest values (PTVs) and prosthesis function were evaluated. In the radiographic evaluation, the distance between implant shoulder and first crestal bone-implant contact (DIB) in mm and the horizontal bone loss (HBL) in mm were measured. The relatively high mPI scores (mean, 0.82; score, 0 in 44.4%; SD, 0.83) did not result in increased SFFR scores (mean, 12; min, 3, max, 38; SD, 7.43) or higher mBI scores (mean, 0.35; score, 0 in 70.8%; SD, 0.59), which was commensurate with healthy peri-implant mucosa. A mean PD value of 2.15 mm (min, 1 mm; max, 5 mm; SD, 0.96) and a mean DIM value of 0.28 mm (min, 0 mm; max, 2 mm; SD, 0.52) were measured. The implants were stable, showing a mean Periotest value of -1.91 (max, 02, min, -6; SD, 1.76). A mean DIB of 3.19+/-0.95 mm (range, 1.3-5.16 mm) and a mean HBL of 1.6+/-1.52 mm (range, 0.28-8.33 mm) were calculated. A correlation was found between DIB and the parameters SFFR (P=0.060), DIM (P=0.042), AL (P=0.050) and especially PTV (P<0.01), leading to the assumption that these clinical parameters may be useful indicators of peri-implant bone loss. The results of the 10-year follow-up examination show that non-rigid telescopic connectors with two interforaminal implants for overdenture stabilization appear to be an efficient and effective long-term treatment modality in severely resorbed edentulous mandibles. Particularly in geriatric patient treatment this concept may provide advantages in terms of handling, cleaning and long-term satisfaction.

Aged↗
PubMed1982

A comparative evaluation of two fiberoptic bronchoscopy catheters: the plugged telescoping catheter versus the single sheathed nonplugged catheter.

We prospectively evaluated the ability of the plugged telescoping catheter (PTC) brush and the single sheathed nonplugged catheter brush to provide sterile lower respiratory tract samples during fiberoptic bronchoscopy in 19 noninfected patients with cancer. Both brushes were evaluated, in random order, in each of the 19 patients. The PTC brush and the single sheath brush were sterile in 12 and 5 patients, respectively, and in 7 patients, the PTC brush alone was sterile (p = 0.016, two-sided). Patients were anesthetized by lidocaine administered through the bronchoscope (6 patients), via an aerosol (3 patients), or by transtracheal injection (10 patients). The advantage of the PTC brush was evident only when aerosol or transtracheal anesthesia were used; the PTC brush was sterile in 9 of 13 patients, whereas the single sheathed brush was sterile in only 2 of these 13 (p = 0.016, two-sided). The plugged telescoping catheter brush is therefore more suitable than the single sheathed brush catheter for delivering sterile brushes to the lower respiratory tract during fiberoptic bronchoscopy.

Aerosols↗
PubMed1989

Video nasopharyngoscopy: a comparison of fiberscopic, telescopic, and microscopic documentation.

Video nasopharyngoscopy is a most valuable method of documenting the anatomy and pathophysiology of the nasopharynx. Such a permanent record is useful for diagnosis, patient counselling, resident teaching, and the monitoring of therapy in nasopharyngeal disorders. To evaluate the various techniques for assessment of the nasopharynx, the authors have attempted to systematically compare flexible and rigid endoscopes and mirror examination during video recording. The pros and cons of 1) transnasal fiberscopic, 2) transnasal telescopic, 3) transoral telescopic, and 4) transoral microscopic mirror examination methods for video nasopharyngoscopy are discussed.

Adolescent↗
PubMed1999

Telescopic video microlaryngeal surgery.

Although traditional microscopic laryngeal surgery has been well developed, we still may encounter some clinical problems, including exposure difficulty, blind areas during examination, and inadvertent cutting through lesions. These problems may lead to an increased risk of complications or protracted or even repeated operations. We have partially overcome these problems since October 1992 with a new telescopic endolaryngeal surgery technique. This technique was developed by combining and modifying the principles of bronchoscopic surgery and endoscopic sinus surgery. With this technique, it is not necessary to use a very slim laryngoscope or apply overpressure on the larynx when introducing and suspending the laryngoscope. Difficult-to-examine regions can be accessed more easily. We can also get a 3-dimensional impression of lesions and related structures, so it is easier to determine a proper cutting line to avoid cutting through lesions. We consider this telescopic method to be a useful alternative to conventional microscopic laryngeal surgery.

Adult↗
PubMed1984

Telescoping osteotomy for pressure metatarsalgia.

A review is presented of 508 feet in 310 patients after telescoping osteotomy of the lesser metatarsals for metatarsalgia. The patients were predominantly female (80%), with a mean age of 55 years; the range of follow-up was 1 to 12 years. In 22% of the patients the metatarsalgia was associated with rheumatoid arthritis. Improvements in assessment and modifications in technique are reported and the management of complications is discussed. The results show that telescoping osteotomy for established cases of pressure metatarsalgia is a simple and reliable operation. Permanent relief of symptoms can be expected in over 80% of patients.

Adult↗
PubMed2002

Seventeenth-century telescope optics of Torricelli, Divini, and Campani.

Optics of telescope makers Torricelli, Divini, and Campani dating back to the 17th century have been tested interferometrically. It was found that the optical polishing technology had progressed to thorough control over the surface figure and finish, while the nearly paraxial conditions of the aperture remained constant. The instruments that were examined exemplify the knowledge of optics of that time, particularly with respect to the early use of erector units in terrestrial telescopes.

Journal Article↗
PubMed2002

Interferometric hartmann wave-front sensing for active optics at the 6.5-m conversion of the multiple mirror telescope.

A little-used interferometric modification to the classical Hartmann optical test is being used for active optics corrections at the 6.5-m Multiple Mirror Telescope (MMT) Observatory. The technique produces compact interference spots whose positions depend on discrete wave-front phase-difference errors. A diffraction model illustrates the formation of interference spots. The limitations on wave-front sampling that are due to atmospheric seeing are estimated. Two data reduction matrix strategies are given. A single correction of collimation and primary mirror figure produces a nearly diffraction-limited telescope image. Wave-front polynomial coefficients ranging from several nanometers to several micrometers in amplitude are reliably detected.

Journal Article↗
PubMed2002

Comparison of designs of off-axis Gregorian telescopes for millimeter-wave large focal-plane arrays.

We compare the diffraction-limited field of view (FOV) provided by four types of off-axis Gregorian telescopes: the classical Gregorian, the aplanatic Gregorian, and the designs that cancel astigmatism and both astigmatism and coma. The analysis is carried out with telescope parameters that are appropriate for satellite and balloonborne millimeter- and submillimeter-wave astrophysics. We find that the design that cancels both coma and astigmatism provides the largest flat FOV, approximately 21 square deg. We also find that the FOV can be increased by approximately 15% by means of optimizing the shape and location of the focal surface.

Journal Article↗
PubMed2003

Step-zoom dual-field-of-view infrared telescope.

The design of a dual-field-of-view telescope for an 8-12-microm imaging waveband is described. Preliminary calculations are made to determine the first-order parameters of the narrow- and the wide-field modes. To achieve a switchable dual-field-of-view system, one use an optical configuration based on the axial motion of a single lens group along the optical axis. The same lens is also used for focusing at near objects and for athermalization by small axial movement. A total of six lenses with one conic surface are used in the design, making the telescope cost effective and lightweight. The final optical design is presented, along with the aberrations curves and modulation transfer function plots, showing excellent performance in both fields of view.

Journal Article↗
PubMed2003

Diffraction effects from giant segmented-mirror telescopes.

Ultrahigh contrast imaging with giant segmented-mirror telescopes will involve light levels of order 10(-6) times that of the central diffraction spike or less. At these levels it is important to quantify accurately various diffraction effects, including segmentation geometry, intersegment gaps, obscuration by the secondary mirror and its supports, and segment alignment and figure errors. We describe an accurate method for performing such calculations and present preliminary results in the context of the California Extremely Large Telescope.

Journal Article↗
PubMed2003

Numerical simulations of multiconjugate adaptive optics wave-front reconstruction on giant telescopes.

We present sample Monte Carlo simulation results to illustrate the trends in multiconjugate adaptive optics (MCAO) performance as the telescope aperture diameter increases from 8 to 32 m with all other first-order system parameters held constant. The MCAO system considered includes three deformable mirrors, a 1-arc min square field of view, and five wave-front-sensing references consisting of either natural guide stars or laser guide stars at a range of either 30 or 90 km. The rms residual wave-front error decreases slowly with increasing aperture diameter with natural guide stars, whereas performance degrades significantly with increasing aperture diameter for laser guide stars at 30 km if the number of guide stars is held fixed. Performance with laser guide stars at 90 km is a weak function of telescope aperture diameter in the range from 8 to 32 m, with rms wave-front errors no more than 20% greater than the corresponding natural guide-star case for the same level of wave-front sensor's measurement noise.

Journal Article↗
PubMed2004

Model of image degradation due to wind buffeting on an extremely large telescope.

A parametric model of wind buffeting on an extremely large telescope with a multipod secondary support is described. The model estimates wave-front errors that are due to wind buffeting on a segmented primary, wind-induced secondary figure and position errors, and primary-mirror deformations caused by wind forces on the secondary support. The approach is based on a Zernike expansion of pressure fluctuations, with simple models of stiffness, resonance, and control. The model shows that wind buffeting on a multipod attached to the primary mirror cell significantly degrades the image quality in a large telescope with a slow primary.

Journal Article↗
PubMed2004

Location of the elevation axis in a large optical telescope.

Proposed designs for the next generation of large optical telescopes favor a tripod or quadrupod secondary support, and a primary supported from the back, but it is not yet clear whether the elevation axis should be in front of the primary or behind it. A study is described of the effect of elevation-axis location on key performance parameters (fundamental frequency, blockage, and wind-induced secondary decenter) for a 30-m Cassegrain telescope with amount configuration that is typical of the new designs. For a fast (e.g., f/1) primary, the best location for the elevation axis is behind the primary. The penalty for moving the elevation axis in front of the primary is roughly a 40% decrease in fundamental frequency and a corresponding reduction in the control bandwidth for pointing and optical alignment.

Journal Article↗
PubMed2004

Control and alignment of segmented-mirror telescopes: matrices, modes, and error propagation.

Starting from the successful Keck telescope design, we construct and analyze the control matrix for the active control system of the primary mirror of a generalized segmented-mirror telescope, with up to 1000 segments and including an alternative sensor geometry to the one used at Keck. In particular we examine the noise propagation of the matrix and its consequences for both seeing-limited and diffraction-limited observations. The associated problem of optical alignment of such a primary mirror is also analyzed in terms of the distinct but related matrices that govern this latter problem.

Journal Article↗