Thick Skins Research Articles

Impact perforation of sandwich panels with aluminum foam core: A numerical and analytical study

This paper tends to study the observed piercing force of sandwich panels with foam cores under impact loading by numerical and analytical methods. For this purpose, numerical models are built using LS-DYNA and calibrated with the inversed perforation test instrumented with an instrumented pressure bar on the AlSi7Mg0.5 Aluminum foam core sandwich panels with 0.8 mm thick 2024T3 Aluminum top and bottom skins. Actually, the proposed numerical model can predict piercing force vs. displacement curves in good agreement with experimental measurements (tests at impact velocities at 27 and 44 m/s). More confidence is obtained by the fact that the simulation can also reproduce the failure mode of the top skin and bottom skin.Virtual tests using this numerical model are conducted with higher impact velocities up 200 m/s. A continuous increase of the piercing force of top skin with impact velocity is found. A careful analysis of numerical results (difference between top and bottom skin perforation, stress level beneath the top skin, etc.) shows that the foam core strength enhancement due to shock front propagation is responsible for this piercing force increase under impact loading.Finally, an analytical model using an improved RPPL shock model based on a power law densification assumption is proposed to calculate the top skin piercing forces. This analytical model provides a prediction in good agreement with the experimental and FE results in a large range of impact velocities.

Central counterparties need thicker skins

Central counterparties need thicker skins

Response of yams exposed to different sources and doses of nitrogen fertilizers in the State of Maranhão, Brazil

This study was carried out at the State University of Maranhão, São Luís, Brazil from January to November 2012. We assessed the behavior of the yam Dioscorea cayenensis ‘Da Costa’, fertilized with different rates and sources of nitrogen (N). The experimental design was randomized, with treatments in a 6 × 2 factorial design. The factors were represented by six rates of N fertilization (0, 50, 100, 150, 200, and 250 kg·ha-1) and two sources (ammonium sulfate and urea) by using four replicates. We evaluated the mean mass, commercial root yield, leaf N content, starch content in the tubers, and percentage of tubers with symptoms of nematode infection (dry and thick skins). The maximum values for the mean masses of commercial tubers were 2.5 and 1.9 kg with doses of 130 and 160 kg of N ha-1 from ammonium sulfate and urea, respectively. Doses of 130 and 154.3 kg of N ha-1 produced the maximum yields of commercial tubers of 19.7 and 14.9 t·ha-1 with ammonium sulfate and urea fertilization, respectively. The maximum levels of foliar N by using urea and ammonium sulfate were 36.5 and 29.3 g·kg-1, respectively, at a dosage of 250 kg·ha-1. The maximum starch contents of 25.7 and 28.3 % were obtained at doses of 114 and 116 kg of N ha-1 of ammonium sulfate and urea, respectively. The percentage of tubers infected with nematodes was 10% when the N source was urea and 15.6% when the source was ammonium sulfate, both at a dosage of 250 kg·ha-1.

Enhancing Phenolic Maturity of Syrah with the Application of a New Foliar Spray

Climate change is inducing earlier grape ripening, especially in warm vintages. This phenomenon is resulting in unbalanced wines an alcohol concentration that is too high and titratable acidity that is low, along with a high pH level without the desired level of phenolic maturity. Final wine quality notably depends on the phenolic composition of the grapes and the extractability of these compounds. This research was designed to test a new foliar spray, called LalVigne® MATURE, for its capacity to create a balance between sugar development and phenolic maturity. It is a formulation of 100% natural, inactivated wine yeast derivatives. This foliar spray was tested on Syrah vines in two vintages (2012 and 2013) in a cool-climate wine region (Eger, Hungary). The spray acted as an elicitor, stimulating the synthesis of several secondary metabolites. The changes in anthocyanin extractability and texture characteristics of the grape berries were followed during ripening. Experimental wines were made at three separate harvest times in each vintage. Standard analytical parameters were evaluated for grapes and wines, as well as for resveratrol. Grapes from the treated vines had thicker skins than the controls at all sampling dates in both vintages. The phenolic potential (especially anthocyanin concentration and extractability) of the foliar spray-treated grapes was greatly improved. Our experiment showed that phenolic ripening can be enhanced using the foliar spray, and that its application was useful in different vintages.

Hunting on the margins of medieval West African states: a preliminary study of the zooarchaeological record at Diouboye, Senegal

Leather, animal skins and ivory were important components of the economies of medieval West African societies. Despite the prominent role of hunters in diverse oral histories throughout the region, little is known about the actual production of animal products, in particular those derived from wild animals. This paper presents a preliminary examination of the zooarchaeological record of Diouboye, an eleventh- to fourteenth-century AD settlement located along the Falémé River in eastern Senegal. Analyses of a representative sample of the large and diverse faunal assemblage at Diouboye indicate that, in addition to keeping domestic livestock and dogs, the site's occupants hunted large numbers of animals found in riverine ecosystems. In comparison with contemporary West African sites located in similar environmental zones, the economy at Diouboye is particularly focused on medium-sized bovids, animals yielding thick skins and ivory, and carnivores. We argue that this hunting strategy may indicate an emphasis at the site on secondary products, an interpretation strengthened by the excavation of pit features and stone tools that may have been used in the soaking and scraping skins and furs.

Needle-free anaesthesia, a promising option for the needle-phobic patient

Funding sources: None. Conflicts of interest: None declared. Dear Editor, Needle phobia and pain during injection with a needle is often an overlooked obstacle that may impede access to effective healthcare in dermatological procedures. Needle phobia, defined as an intense, persistent and unreasonable fear of needles, affects more than 20% of the population. Needle injection on the thick skins of the palms requires an effective pain management method, particularly during onabotulinumtoxinA (BTX‐A) injections to control intractable palmar hyperhidrosis.1 Peripheral nerve blockade of the wrist, an effective method of alleviating pain during palmar injection may have serious drawbacks, particularly when used repeatedly.2 Moreover, it is time consuming and may affect hand dexterity for many hours. The Bier block technique is also effective, but systemic effects could occur.3 Vibration anaesthesia has been used with inconsistent results.4 Cryoanalgesia can freeze the needle, slowing down the diffusion of the injectate.5 Needle‐free injection, also known as jet injection, is a needle‐free drug delivery method in which a high‐speed stream of fluid penetrates the skin. The use of jet injectors in routine dermatological practice remains low owing to several factors, including the risk of infection, pain and bruising. In our practice, a versatile, low‐pressure needle‐free injector (such as the Med‐Jet® MBX manufactured by MIT Canada, Montreal, QC, Canada) has many applications. Here we describe two cases that illustrate the effective application of a needle‐free injection device for local anaesthesia.

Buckling analysis of stiffened variable angle tow panels

Variable angle tow (VAT) laminates have previously shown enhanced buckling performance compared to conventional straight fibre laminates. In this study, an analytical method is developed for the buckling analysis of a novel blade stiffened VAT panel to allow this potential to be more fully exploited. The prebuckling and buckling analysis, performed on a representative section of a blade stiffened VAT panel, are based on a generalised Rayleigh–Ritz procedure. The buckling analysis includes a first order shear deformation theory by introducing additional shape functions for transverse shear and is therefore applicable to structures with thick skins relative to characteristic length. Modelling of the stiffener is achieved with two approaches; idealisation as a beam attached to the skin’s midplane and as a rigidly attached plate. Comparing results with finite element analysis (Abaqus) for selected case studies, local buckling errors for the beam model and plate model were found to be less than 3% and 2% respectively, whilst the beam model error for global buckling was between 3% and 10%. The analytical model provides an accurate alternative to the computationally expensive finite element analysis and is therefore suitable for future work on the design and optimisation of stiffened VAT panels.

Ultrasonographic evaluation of long‐term results of nasal tip defatting in rhinoplasty cases

Nasal skin thickness has an important role in aesthetic results of rhinoplasty. The aim of this study was to evaluate the long-term results of tip and supratip skin defatting technique in rhinoplasty subjects using ultrasonography. Prospective, randomized, case-control study. Among 111 rhinoplasty cases referred to a university hospital between February 2010 and September 2011, after physical examination and measuring the nasal tip and supratip skin thickness by ultrasonography, a total of 55 patients with thick and moderate skin were randomly allocated for rhinoplasty using one of the following methods: rhinoplasty with (case group) and without (control group) defatting tip and supratip skin. Ultrasonographic evaluation of the skins was repeated 1 and 12 months after surgery, and the data were analyzed by Wilcoxon and repeated measure tests using SPSS 17 software. Twenty-eight of 55 candidates (10 men, 45 women; mean age, 25.1 ± 7.6 years) underwent skin defatting during rhinoplasty; the other 27 patients did not undergo this procedure. Forty-four patients completed the study. Thickness of tip and supratip skin was not statistically different before surgery and during follow-up evaluations in defatting and nondefatting technique groups (P = .7). Defatting techniques have no effect on reducing tip and supratip skin thickness after rhinoplasty in moderate to thick skins.

From Hyperkeratosis to Apoptosis: Lessons Learned from 65 Years of Research

In 1950, shortly after completing my Ph.D. degree requirements and joining the faculty of the Animal Science Department at Cornell University, I heard about X-disease, or, more accurately, bovine hyperkeratosis, from Dr. Kenneth McEntee, a pathologist in the Veterinary College at Cornell. Affected animals developed thick skins, resembling armor plate. This was a consequence of their inability to convert carotene to vitamin A [1]; they lacrimated profusely so that their faces were constantly wet and they lost weight and eventually died. The disease, at first thought to be caused by a virus, was increasing rapidly in the United States and Europe, especially in Germany, prompting the U.S. Department of Agriculture to establish a special research program for the disease. Dr. McEntee and I, along with Dr. Peter Olafson, chairman of the Pathology Department, set out to find the cause of this disease. Luckily, we found some bread crumbs collected from beneath the slicer in a bakery in Burlington, VT, that had been fed to calves that later developed the disease. We extracted the active compound with ether and subjected the extract to column chromatography, testing each fraction for potency by monitoring plasma levels of vitamin A in test calves. Finally, we were able to crystallize the active compound(s) and identify them by spectrophotometry as highly chlorinated naphthalenes [2]. These compounds had been added to heat-resistant lubricants and fire-retardant paints and were also found in a wood preservative made in Germany. When these discoveries were published, and the napthalenes were removed, the disease rapidly disappeared, and few scientists today have ever heard of it. In retrospect, this early research achievement was a great morale booster, at a critical time in my career. My major research project—the measurement of steroids and gonadotropins in blood and tissues of cattle—was floundering. Plasma levels of steroids, particularly estrogens, proved to be lower than found in other species, and the methods we were using (differential extractions followed by column chromatography and measurement by spectrophotometry) were not adequate. The first comprehensive data correlating plasma luteinizing hormone (LH), estrogen, and progesterone levels during the bovine estrous cycle were not published until 1972 [3]. The Lesson Learned

Forced Convection Heat Transfer in Spray Formed Copper and Nickel Foam Heat Exchanger Tubes

A thermal spray coating process was used to deposit dense 2 mm thick metal skins on the surfaces of square cross-section channels (300 mm × 20 mm × 20 mm) of nickel and copper foams with 10 and 40 PPI (pores per inch) pore densities. A heater was wrapped around the channels to apply surface heat-fluxes varying from 427 to 6846 W/m2. Compressed air was blown through the channels at flow rates of 5–80 l/min. Foam and fluid temperature distributions along the length of the channel and the pressure drop across it were measured. The foam was modeled as a porous medium and properties such as permeability K and inertial coefficient CF were determined from the experimental data. Local and average convective heat transfer coefficients were calculated from air and foam temperature measurements. Nusselt numbers were calculated and correlated in terms of the Reynolds, Prandtl, and Darcy numbers. Heat transfer to air flowing through a 10 PPI foam channel was shown to have increased nearly seven times compared to that of hollow tube with the same dimensions.

High-Resolution Ultrasound Imaging to Demonstrate and Predict Efficacy of Carbon Dioxide Fractional Resurfacing Laser Treatment

Fractional resurfacing is a new laser treatment used mainly for treating photoaging and acne scars. To demonstrate the efficacy of carbon dioxide (CO(2) ) fractional resurfacing laser treatment using high-resolution ultrasound imaging and to evaluate factors predictive of response to the treatment. A prospective observational study was undertaken from January 2007 to August 2009. Laser treatment was performed using a CO(2) fractional resurfacing device. Patients were offered high-resolution ultrasound imaging to follow up their treatment. Dermal and subepidermal nonechogenic band (SENEB) thicknesses were measured. Twenty-four consecutive patients were included, allowing follow-up of 107 areas. Statistical analysis showed a significant increase in dermal thickness (mean variation +25.1%, (95% confidence interval=19.0-31.2). SENEB thickness was not changed. Older age and greater initial thickness were associated with a smaller increase in dermal thickness according to multivariate analysis. The region treated was also found to be a significant predictive factor. Smoking, topical anesthesia, severity of local side effects induced by the laser treatment, and phototype were not associated with significant modification of dermal thickness after laser treatment. This is the first report on the use of high-resolution ultrasound imaging to assess the efficacy of fractional laser operating with standard parameters. Increase in dermal thickness was evidenced, possibly explained by collagen neosynthesis or conformational changes in the extracellular matrix component, increasing dermal hydration, although there was no modification of SENEB thickness, suggesting that the skin retains the sequelae of ageing. The treatment appeared to be more effective in younger patients, probably because their fibroblasts are more prone to synthesizing collagen. Thinner skins were more effectively treated than thicker skins because they could be stimulated throughout their thickness with the treatment parameters used.

Poly(vinyl chloride) (PVC) hollow fibre membranes for gas separation

Poly(vinyl chloride) (PVC) gas separation hollow fibre membranes were produced from multicomponent dopes using dry/wet forced convection spinning. Membranes spun from a low polymer content solution exhibited disappointing gas separation properties. Their low selectivities were indicative of thick skins and high surface porosities. In contrast, high polymer content spun fibres showed good gas separation properties. Selectivities were high, active layers relatively thin and surface porosities moderate. Coating with poly(dimethylsiloxane) nullified the surface pores. The favourable performance of the high polymer content spun fibres was also related to shear rate and forced convection residence time during spinning. To the knowledge of the authors, this work represents the first reported success in producing PVC hollow fibre membranes with morphologies suitable for gas separation. The development of PVC hollow fibres relates to the ultimate quest to produce membranes capable of reliably separating oxygen and ozone gas mixtures.

Failure Behaviour of Sandwich Beam Subjected to Projectile Impact

Aerodynamic gun impact test is carried out to investigate sandwich beam with metallic skin and Nomex honeycomb core damage mechanism and failure behaviour. Details of the deformation and damage progression within the sandwich beam are observed in particular. The comparisons between the two kinds of specimen with different thickness skins clearly show that the difference in the impact energy consumed in global bending deformation and the localized indentation. Theoretical elastic bending stiffness of the sandwich beam with thicker skins is approximately 2.26 times greater than that of sandwich beam with thinner skins.

Hybrid processing of thick skins for honeycomb sandwich structures

Carbon–epoxy prepregs are generally used to form the skins of honeycomb sandwich structures used in aerospace or racing yachts. For some applications, it is desirable to increase the thickness of the skins. In order to achieve an ideal core pressure level during cure for maximal skin–core bonding, the issue of air extraction from the honeycomb cells through the skin during processing thus becomes critical, in particular if vacuum only processing is used. In the present work, partially impregnated prepregs, called semipregs, having high initial transverse permeability to air, are combined with traditional prepregs to form a hybrid skin. Results are presented on the pressure change inside the honeycomb cells and the skin permeability to air during cure, as well as on skin–core adhesion. The final sandwich quality is assessed and found to be comparable to that obtained with prepreg skins.

Nanolayer enhancement of biaxially oriented polypropylene film for increased gas barrier

An order of magnitude improvement in the oxygen barrier of biaxially oriented polypropylene (BOPP) films was achieved using a layer-multiplying, forced assembly process. The improvement was achieved without sacrificing clarity and toughness of the films. Sheets with 33 alternating layers of polypropylene (PP) (17 layers) and poly(ɛ-caprolactone) (PCL) (16 layers) were coextruded using layer-multiplication and two thick PP skins were added to the multilayered core as the last step in the continuous coextrusion process. The sheets were subsequently biaxially oriented to draw ratios from 4 × 4 to 6 × 6. Biaxial orientation at elevated temperature reduced the thickness of the melted PCL layers from the microscale to the nanoscale, which created 2-dimensional confinement for subsequent crystallization of the PCL layers. It was anticipated that the PCL layers would recrystallize as highly oriented, in-plane lamellae that would resemble single crystals. However, the PCL lamellae were oriented perpendicular to the film surface, which actually facilitated oxygen permeation through the PCL layers and increased the oxygen permeability of the oriented films. Crystallization as on-edge lamellae was attributed to nucleation by the polypropylene surface. However, the surface nucleation was prevented by inserting buffer polystyrene (PS) layers in between the PCL and PP layers. In this case, the PCL lamellae were oriented in-plane. With the very high aspect ratio lamellar crystals oriented perpendicular to the flux direction, the permeation pathway of oxygen became very tortuous and the oxygen barrier was significantly improved.

Propagation characteristics of laser-induced stress wave in deep tissue for gene transfer

Propagation characteristics of laser-induced stress waves (LISWs) in tissue and their correlation with properties of gene transfection were investigated for targeted deep-tissue gene therapy. LISWs were generated by irradiating a laser-absorbing material with 532-nm Q-switched Nd:YAG laser pulses; a transparent plastic sheet was attached on the absorbing material for plasma confinement. Temporal pressure profiles of LISWs that were propagated through different thickness tissues were measured with a needle-type hydrophone and propagation of LISWs in water was visualized by shadowgraph technique. The measurements showed that at a laser fluence of 1.2 J/cm 2 with a laser spot diameter of 3 mm, flat wavefront was maintained for up to 5 mm in depth and peak pressure P decreased with increasing tissue thickness d; P was proportional to d −0.54. Rat dorsal skin was injected with plasmid DNA coding for reporter gene, on which different numbers of excised skin(s) was/were placed, and LISWs were applied from the top of the skins. Efficient gene expression was observed in the skin under the 3 mm thick stacked skins, suggesting that deep-located tissue such as muscle can be transfected by transcutaneous application of LISWs.

MULTIFUNCTIONAL PHOTOACOUSTIC DIAGNOSIS OF BURN INJURIES

For appropriate treatment of severe burn injuries, noninvasive, real-time diagnosis of the wound status, e.g., injury depth, is required; however, modalities for quantitative evaluation are limited. In this paper, a new method for multifunctional diagnosis of burns based on photoacoustic measurement is described. When a burn wound is irradiated with a short light pulse that is selectively absorbed by blood, the light can efficiently propagate though the injured tissue layer due to occlusion of blood vessels and the light is absorbed by blood in the healthy tissue layer under the wound, emitting a photoacoustic (PA) wave through a thermoelastic process. The PA wave can be detected with an acoustic sensor on the wound and its propagation time provides information on the depth of injury. In addition, PA measurement at dual wavelengths, oxy- and deoxyhemoglobin absorption dominant wavelengths, can provide information on local hemodynamics, which is also important for wound management. The validity of these techniques was demonstrated by experiments using rat burn models. Furthermore, applicability of this measurement to thick burned skins was examined by experiments using a thick burn mimicking model. The results suggest that the present PA diagnosis technique can be applied to human skin burns.

Optimum shapes for minimising bond stress in scarf repairs

Bonded scarf repairs are used in composite structures when high strength recovery is needed or when there is a requirement for a flush surface to satisfy aerodynamic or stealth requirements. However, scarf repairs are complex to design and require the removal of significant parent structure, particularly for thick skins. In this investigation, analytical and numerical approaches have been developed to investigate whether an optimum repair shape for a known biaxial load can be determined. The results clearly demonstrate that the strength of a repaired panel can be improved by optimising both the initial damage cut-out shape and the scarf angle distribution.

Investigation of Parameters Governing the Damage and Energy Absorption Characteristics of Honeycomb Sandwich Panels

Honeycomb sandwich panels of various skin thicknesses and core densities have been investigated under quasi-static loading in bending and indentation with both hemispherical (HS) and flat-ended (FE) indenters. Core crushing, top skin delamination, and top skin fracture are identified as major damage mechanisms. Their characteristics and energy-absorbing capabilities are established using load—displacement and load—strain curves and inspections of cross-sectioned specimens. The effects of varying skin thickness, core density and type, indenter nose shape, and boundary conditions on the damage and energy-absorbing characteristics are examined. The variation of the indenter nose shape is shown to induce a change in the damage mechanisms and have the most significant effect on energy absorption, especially for panels with relatively thicker skins. Increasing the skin thickness significantly increases not only the initial threshold and ultimate loads but also the absorbed energy (AE) of the panels. Increasing the core density has a very small effect on either the ultimate loads or the energy-absorbing capacity, while the effect of the support conditions on the damage and energy-absorbing characteristics is small. The larger 220 mm diameter panels absorb significantly more energy than the 100 mm diameter panels because of the much greater ultimate displacement. Different core materials with a similar density show little difference in either the damage or the energy-absorbing characteristics due to the limited contribution of transverse shear resistance. Panels with a delaminated top skin have lower threshold loads under both indenters and lower ultimate load for the HS indenter.

Handouts in the Classroom: Is Note Taking a Lost Skill?

Handouts in the Classroom: Is Note Taking a Lost Skill?