Good Handling Characteristics Research Articles

Photochemical decomposition of trisoxalatoiron(III): A hydrometallurgical application of daylight

As part of a study of oxalic acid leaching to reduce the iron content of glass sand, photochemical reduction of trisoxalatoiron(III) species formed in the leachates and precipitation of the product as iron(II) oxalate dihydrate were examined as potential means of treating process liquors. Parametric studies showed that, under favourable conditions — including concentration (80–700 mg/l Fe, 1–2% w/v oxalic acid), quality and intensity of illumination (e.g., daylight of illumination > 2500 lux), temperature (ambient), mode and intensity of agitation (slow stirring), and pH (<2) — the primary reaction (reduction of iron(III) to iron(II) with evolution of carbon dioxide from oxalate) largely occurred within 1–2 h. Following an induction period of several h during which the solution became supersaturated with respect to iron(II) and oxalate, well-formed yellow 10–40 Am crystals of FeC 2O 4 · 2H 2O (matching those reported in the literature) were precipitated over about 24 h. An excess of oxalic acid was necessary to maximise the rate of photochemical reaction and minimise re-oxidation (which caused an increase in pH and led to the precipitation of hydrated iron(III) oxide). For both thermodynamic and kinetic reasons, the extent of reaction was normally restricted to about 80% of the theoretical maximum. Photodecomposition was shown to be a potential continuous hydrometallurgical process meriting more detailed evaluation. Because of its relatively high purity and good handling characteristics, the precipitated iron(II) oxalate dihydrate represented a useful potential feedstock for added-value products, e.g., speciality iron oxides.

A completely biological tissue-engineered human blood vessel.

Mechanically challenged tissue-engineered organs, such as blood vessels, traditionally relied on synthetic or modified biological materials for structural support. In this report, we present a novel approach to tissue-engineered blood vessel (TEBV) production that is based exclusively on the use of cultured human cells, i.e., without any synthetic or exogenous biomaterials. Human vascular smooth muscle cells (SMC) cultured with ascorbic acid produced a cohesive cellular sheet. This sheet was placed around a tubular support to produce the media of the vessel. A similar sheet of human fibroblasts was wrapped around the media to provide the adventitia. After maturation, the tubular support was removed and endothelial cells were seeded in the lumen. This TEBV featured a well-defined, three-layered organization and numerous extracellular matrix proteins, including elastin. In this environment, SMC reexpressed desmin, a differentiation marker known to be lost under standard culture conditions. The endothelium expressed von Willebrand factor, incorporated acetylated LDL, produced PGI2, and strongly inhibited platelet adhesion in vitro. The complete vessel had a burst strength over 2000 mmHg. This is the first completely biological TEBV to display a burst strength comparable to that of human vessels. Short-term grafting experiment in a canine model demonstrated good handling and suturability characteristics. Taken together, these results suggest that this novel technique can produce completely biological vessels fulfilling the fundamental requirements for grafting: high burst strength, positive surgical handling, and a functional endothelium.

The Effect of Polyamic Acid Binder Concentration on the Processability and Properties of LaRC TPI Composites Made by Suspension Prepregging

Unidirectional carbon fiber/LaRC TPI composites were prepared by aqueous suspension prepregging. The matrix material was fully imidized LaRC TPI powder, and the binder was LaRC TPI polyamic acid. The effect of the concentration of the polyamic acid binder on composite processability and properties was studied. An optimum concentration range of 2.9-9.4% weight/weight binder/matrix was found that resulted in good prepreg handling characteristics and good consolidation. A binder concentration 2 13.1% led to poorer consolidation of the composites due to an increase in the melt viscosity of the matrix. This increase was probably due to a combination of crosslinking and chain extension of the polyamic acid during the imidization step. Formation of the crosslinked structure was supported by transverse flexure, meso-indentation, and solubility tests.

Carbodiimide cross-linked gelatin: a new coating for porous polyester arterial prostheses

The performance of a polyester arterial prosthesis impregnated with gelatin and cross-linked with carbodiimide (Uni-graft ®) was compared with its porous parent graft (Protegraft ®) using a canine thoraco-abdominal bypass model. The grafts were investigated in terms of their handling characteristics, imperviousness at implantation, surface thrombogenicity and healing behaviour. Prostheses 30 cm in length were implanted for the following periods: 4, 24 and 48 h, 1, 2 and 4 weeks, 2, 3, 4, 5 and 6 months. Both types of graft had good handling characteristics. The ready-to-use impregnated graft provided satisfactory haemostasis at implantation with no blood permeating through the wall after flow was restored. Both grafts exhibited low surface thrombogenicity, as determined by the uptake of labelled fibrin and platelets, and the healing sequence of the impregnated graft after resorption of the gelatin was equivalent to that of the preclotted control. Biodegradation of the gelatin was complete within 1 month of implantation with the subsequent development of a collagenous internal capsule at both anastomoses. Endothelial cells were observed between 4 and 6 months, but were confined to small islets distributed along the luminal surface. The prostacyclin/thromboxane A 2 ( PGI 2 TXA 2 ) ratio, which gives an indication of the level of endothelial cell activity, was greater than 1.0 after 1 week of implantation for the control graft. For the impregnated graft it reached 1.0 only after 3 months of implantation, but remained above 1.0 for periods of up to 6 months. In conclusion, the impregnated graft experienced first a biodegradation of the gelatin coating which then gave way to a similar healing sequence to that of the preclotted prosthesis.

Why Make Monofilament Sutures Out of Polyvinylidene Fluoride?

In recent years some clinical reports have associated suture failures with polypropylene monofilaments. Therefore there is interest in developing an alternative suture material that is less thrombogenic than polyester and similar in handling characteristics but less prone to mechanical failure than polypropylene. To this end, Peters Laboratoire Pharmaceutique has developed a new monofilament suture material from polyvinylidene fluoride (PVDF), which has been subjected to a special treatment to modify its crystalline form and level of crystallinity. The purpose of this study was to evaluate its mechanical, chemical, and biologic properties and to compare its performance, in a peripheral vascular application, to that of a polypropylene control. A series of in vitro tests were performed to study the morphology, tensile properties, creep, surface chemistry, thermal characteristics, and resistance to iatrogenic trauma. In addition, an in vivo trial was undertaken in which vascular prostheses anastomosed with either PVDF or polypropylene sutures were implanted as a thoracoabdominal bypass for 6 months in the dog. Histologic and degradation analyses were performed on the explants. The results from the mechanical tests on 4-0, 5-0, and 6-0 PVDF and polypropylene sutures demonstrated that although both materials have similar breaking strengths, the PVDF has a higher extension at break, has less delayed extension when under tensile creep testing, and suffers less trauma than the polypropylene when compressed by a standard needle holder. While chemical analyses found evidence of surface oxidation on both types of sutures, thermal analysis confirmed that the level of crystallinity of the PVDF polymer is higher than that of the polypropylene control. During the pilot study in animals, PVDF sutures were found to have good handling and frictional characteristics that facilitated the tying of knots. Histologic analysis of the explants found no inflammatory cells in the tissue surrounding either the PVDF or polypropylene sutures, and scanning electron microscopic examination of the cleaned suture surfaces found no evidence of degradation during 6 months in vivo. Though preliminary in nature, these findings indicate that monofilament sutures made from PVDF provide an attractive alternative to those made from polypropylene for use in cardiovascular surgery. In addition to providing acceptable in vivo behavior and being easy to manipulate and more resistant to iatrogenic injury, PVDF materials can be sterilized by beta or gamma radiation and so can reduce dependence upon ethylene oxide and chlorofluorohydrocarbons.

Autologous fibrin glue for sealing vascular prostheses of high porosity.

Thirty high-porosity double-Velour vascular prostheses were sealed with fibrin glue, the fibrinogen in the glue being prepared from citrated plasma by ethanol precipitation. After such preparation the prostheses were blood-tight at a pressure > 300 mmHg. Using a fibrin concentration of 13 mg/ml (obtained by dilution of the fibrinogen solution) the prostheses were blood-tight at a minimum pressure of 150 mmHg, which is suitable for clinical use. Sufficient fibrin glue can be prepared from 44-88 ml of the patient's blood to seal most types of high-porosity vascular prosthesis used clinically. The fibrin-sealed grafts have good handling characteristics because they are soft, pliable and non-sticky. The use of autologous fibrin glue has obvious safety advantages by preventing both transmission of viral diseases and immunological reactions.

Porosity of Various Preparations of Acrylic Bone Cements

The total porosity and mean pore sizes of various bone cement preparations were measured using image analysis. The porosity in different commercial bone cements varied from 5% to 16% when these cements were prepared in the usual fashion. Centrifugation for 30 seconds resulted in a substantial reduction in the overall porosity of Simplex P, AKZ, Zimmer Regular, and CMW bone cements by reducing both the mean pore size and the number of pores per unit area. In contrast, the porosity of LVC, Palacos R, and Palacos R with gentamicin bone cements was not significantly decreased by centrifugation. Chilling the monomer before mixing resulted in higher porosity of both the centrifuged and uncentrifuged Simplex P, Zimmer Regular, and CMW bone cements. Simplex P mixed with chilled monomer and centrifuged for 120 seconds has one of the lowest porosities of the various cements, while retaining good handling characteristics and excellent fatigue strength.

Polyethylene-Lead Tissue Compensators for Megavoltage Radiotherapy

Tissue compensators afford one the opportunity of producing idealized dose distributions in radiotherapy. We have developed a technique which may be used to produce fast, accurate and inexpensive compensators within a few minutes and requires minimal patient involvement. Three dimensional contour data is acquired using a moire fringe photograph taken at the time of simulation. The photograph is projected to the size needed for the actual compensator and a sketch of the compensator is made. The sketch is placed in a specially designed small portable pantographic unit and the design is traced while the unit cuts the compensator from an indexed polyethylene-lead blank which is premounted on an acrylic tray. The polyethylene-lead material proves to have an ideal combination of properties for compensator construction including relatively high density, ease of machining, good handling characteristics and low cost.

In vitro and in vivo characterization of an impervious polyester arterial prosthesis: the Gelseal Triaxial® graft

Over the years, textile polyester arterial prostheses have acquired an excellent reputation for easy handling and good healing characteristics. Until recently, the main drawback in using them was the need for preclotting. This, however, is no longer true. Nonporous polyester grafts which have been coated with an impervious bioerodible layer during manufacture are now commercially available. The Gelseal Triaxial® prosthesis is one of this new generation of grafts. It is manufactured by impregnating a Triaxial® prosthesis with a gelatin coating. An in vivo and in vitro evaluation of this new device has found that its water permeability is almost zero. It has good handling and conformability characteristics, and its bursting strength is slightly greater than that of the uncoated prosthesis due, no doubt, to the presence of the gel. The rates of degradation of the gelatin coating have proven to be rapid under both in vitro and in vivo conditions. In fact, only a few traces of the gel were found remaining on the graft after 2 wk in the canine thoracic aorta. In addition, this study has demonstrated that the use of a bioerodible gelatin coating, with its ability to promote cellular regeneration, is a feasible approach with which to achieve earlier and more complete biological healing.

Paper Material Considerations for System Printers

Laser printing of continuous forms by means of electrophotographic imaging requires that the paper on which the printing is carried out show good handling characteristics at fast machine speeds and be compatible with toner transfer and fixing. Toner transfer requires suitable electrical paper characteristics, similar to those of xerographic cut sheets intended for use in electrophotographic cut-sheet copiers and printers. Hot-pressure fusing in the IBM 3800 printing subsystem has been shown to require adequate paper-fiber wettability by the hot molten toner. Therefore, characteristics of paper chemistry, and in particular paper sizing, are essential in creating good image fixing (fusing). In addition, the temperature and pressure in the fusing assembly affect the thermal and dimensional stability of the paper. For the 3800, this necessitated modifications in roll design within the fusing station in order to ensure satisfactory paper handling.

A New DAP-Polyester Resin for Carbon Fibers

Epoxy resins are the primary matrix materials used in carbon fiber composites, and prepreg systems made with these epoxies offer good handling characteristics and good ambient and elevated temperature properties. However, epoxy resins do have certain deficiencies in that the prepreg materials must be kept refrigerated, cost is higher than other available thermoset materials, and cure time is often long.

Optimising the shape

THE ECONOMIC and operational efficiency of any supersonic airliner depends on the successful reconciliation of two conflicting aerodynamic requirements: good control and handling characteristics at subsonic and transonic speeds and low trim drag at supersonic speeds. Years of aerodynamic research have established the slender delta wing as the optimum shape for mach two cruise. In the Concorde design, the basic slender delta was modified by cambering the profile and tapering the forward part of it, refining the wingtips and leading edges to give improved low speed controllability without detriment to supersonic performance. Thousands of hours in different wind tunnels have enabled optimisation of the shape of the aircraft. Some results which were not available in time for incorporation on the prototypes have already been embodied on the pre‐production and production planes. Even though some of these modifications, such as elongation, redesigned nose vizor and tail shape were not applied for aerodynamic improvements, they have nevertheless affected aerodynamics.

HS 1182 — design for defence in the 1980's

THE HS 1182 multi‐purpose ground attack‐trainer has been designed to offer good handling characteristics throughout its flight envelope, slow approach and landing speeds suitable for the basic jet training requirement and high indicated air speed and mach number performance necessary for the advanced flying training stage. This ensures the aircraft will embrace the wide spectrum currently covered by the Gnat/Hunter and Jet Provost.

PIEZOELECTRIC PROPERTIES OF Ba2 NaNb5 O15

Single-crystal Ba2NaNb5O15 (z plate) has been found to have a piezoelectric coupling factor in the thickness longitudinal mode kt equal to 0.57. As a value of kt determined by direct measurement, this result is the highest value yet reported for a single-crystal ferroelectric material usable at and above room temperature. Since this material has good mechanical handling characteristics, a relatively low dielectric constant (ε33S/ε0 = 30), and a pure mode of vibration, plates of this material are attractive for applications as high-frequency longitudinal mode transducers. The approximate values of the thickness shear mode coupling factors for x and y plates are k15 = 0.20 and k24 = 0.20.

Aircraft Systems

THE Skyvan is designed for single pilot operation and control about all three axes is provided by conventional manually‐operated controls. The mass‐balanced control surfaces are operated by reversible control circuits to provide a feed back of aerodynamic forces to the pilot whereby good handling characteristics are achieved without the need for any form of artificial feel. Locks in each primary circuit hold the surfaces in the neutral position when the aircraft is parked. The primary control circuits are composed of push‐pull rods which are made from light alloy to avoid differential thermal expansion problems. In the design of all flying control components, safeguards are built in to ensure that not only is it impossible to make a cross connexion, but it is equally impossible to assemble parts inadvertently in a way that would result in restricted travels, reduced gearing or incorrect rigging. The use of ball and roller bearings is confined to critical low friction loss pivots only; at other non‐critical pivots plain bearings are fitted for simplicity, low cost and weight saving. For reliable performance and minimum maintenance requirements, oil‐impregnated plain bearings are fitted whilst ball and roller bearings are pre‐packed with lubricant and scaled.