Abstract
BACKGROUND:
In spinal cord stimulation for the management of chronic, intractable pain, a satisfactory analgesic effect can be obtained only when the stimulation-induced paresthesias cover ...all painful body areas completely or partially.
OBJECTIVE:
To investigate the effect of stimulus pulse width (PW) and contact configuration (CC) on the area of paresthesia (PA), perception threshold (VPT), discomfort threshold (VDT), and usage range (UR) in spinal cord stimulation.
METHODS:
Chronic pain patients were tested during a follow-up visit. They were stimulated monopolarly and with the CC giving each patient the best analgesia. VPT, VDT, and UR were determined for PWs of 90, 210, and 450 microseconds. The paresthesia contours at VDT were drawn on a body map and digitized; PA was calculated; and its anatomic composition was described. The effects of PW and CC on PA, VPT, VDT, and UR were tested statistically.
RESULTS:
Twenty-four of 31 tests with low thoracic stimulation and 8 of 9 tests with cervical stimulation gave a significant extension of PA at increasing PW. In 14 of 18 tests (low thoracic), a caudal extension was obtained (primarily in L5-S2). In cervical stimulation the extension was predominantly caudal as well. In contrast to VPT and VDT, UR is not significantly different when stimulating with any CC.
CONCLUSION:
PA extends caudally with increasing PW. The mechanism includes that the larger and smaller dorsal column fibers have a different mediolateral distribution and that smaller dorsal column fibers have a smaller UR and can be activated only when PW is sufficiently large. A similar effect of CC on PA is unlikely as long as electrodes with a large intercontact distance are applied.
Tribological studies were carried out with tetrahedral amorphous diamond-like carbon (ta-C DLC) coatings, varying in thickness and roughness, using two different contact configurations lubricated ...with seven types of hydraulic oils. Tribopair of cast iron and ta-C coated steel were tested in both non-conformal and conformal, unidirectional sliding contacts. The friction and wear results were mainly affected by the thickness of the coating in the non-conformal contact and the surface roughness of the coating in the conformal contact. Tests done with mineral base oil containing rust inhibitor in the non-conformal contact and with Polyalphaolefins and synthetic ester base oils in the conformal contact resulted in the lowest friction while that with mineral base oil containing zinc resulted in high friction and counterface wear. The results highlight the interdependence of contact configuration, lubricant chemistry, coating’s surface morphology and coating’s thickness in determining the tribological behaviour of ta-C coatings under boundary lubrication.
Display omitted
•Large crystalline domains of TIPS pentacene were prepared by ESD.•We fabricated BC-OFETs based on single-crystalline domains of TIPS pentacene.•The devices exhibited high mobilities, ...but resulted in high threshold voltages.•The threshold voltage could be lowered by reducing the thickness of BC electrodes.
Large crystalline domains (a few hundred micrometers in size) of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) were prepared by electrostatic spray deposition (ESD) and used as the active layers of bottom-contact organic field-effect transistors. The TIPS pentacene active layers were directly patterned via a shadow mask in the ESD process. The device, which had a 5-μm-long channel composed of a single-crystalline domain, exhibited a high field-effect mobility of more than 0.1cm2/Vs but resulted in a high threshold voltage of −17V. The threshold voltage could be lowered to −6.4V by reducing the thickness of the BC electrodes from 30 to 10nm; this threshold voltage lowering was probably due to an improvement in the charge injection from the source electrode to the active layer.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A fretting fatigue life estimation method that takes into account the stress gradient effect was developed by the authors Journal of Mechanical Science and Technology, 28 (2014) 2153-2159. In the ...developed method, fatigue damage value at the cracking location is corrected with fatigue damage gradient and the corrected value is compared directly with the plain fatigue data for life estimation. In other words, the correction factor is the ratio of plain fatigue damage to fretting fatigue damage at the same life and a function of fatigue damage gradient. Since reliability of the method was verified only for cylinder-on-flat contact configuration in the previous study, the present study extends application of the method to flat-on-flat contact configurations by developing the correction factor for both the contact configuration. Fretting fatigue experiments were conducted to obtain fatigue life data for various fretting pads. Finite element analyses were conducted to evaluate the Smith-Watson-Topper (SWT) fatigue damage parameter in the cracking region. It is revealed that the SWT parameter in fat-on-flat contact configuration decreases exponentially away from the surface as in cylinder-on-flat contact configuration, and thus the SWT gradient at the surface can be evaluated reliably. Moreover, it is found that decrease in the SWT parameter around the cracking location can be expressed by piecewise exponential curves. If the gradient of SWT at the surface is used as a representative value of SWT gradient, it is impossible to establish functional relationship between the SWT gradient and the correction factor for both the contact configurations although it was possible for cylinder-on-flat contact configuration. However, if weighted average of the SWT gradient values obtained from each exponential curve in the piecewise exponential curve is used as a representative value, the correction factor for both the contact configurations becomes a function of the SWT gradient, and thus fretting fatigue life in both the contact configurations can be estimated with a single correction function.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Sacral nerve stimulation (SNS) is an established treatment for faecal incontinence involving the implantation of a quadripolar electrode into a sacral foramen, through which an electrical stimulus is ...applied. Little is known about the induced spread of electric current around the SNS electrode and its effect on adjacent tissues, which limits optimisation of this treatment. The authors constructed a 3-dimensional imaging based finite element model in order to calculate and visualise the stimulation induced current and coupled this to biophysical models of nerve fibres. They investigated the impact of tissue inhomogeneity, electrode model choice and contact configuration and found a number of effects. (i) The presence of anatomical detail changes the estimate of stimulation effects in size and shape. (ii) The difference between the two models of electrodes is minimal for electrode contacts of the same length. (iii) Surprisingly, in this arrangement of electrode and neural fibre, monopolar and bipolar stimulation induce a similar effect. (iv) Interestingly when the active contact is larger, the volume of tissue activated reduces. This work establishes a protocol to better understand both therapeutic and adverse stimulation effects and in the future will enable patient-specific adjustments of stimulation parameters.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Fretting fatigue tests are typically performed using either a flat-on-flat or a cylinder-on-flat contact configuration. To obtain a better understanding of the behavior of these two configurations, ...both contact configurations were imposed simultaneously on opposite sides of a fretting fatigue specimen under the same nominal contact load. The evolution of the surface and subsurface damage on both sides was characterized by measuring the frictional force/displacement hysteresis, and by post-test examination with a scanning electron microscope (SEM). Tests were performed on PH 13-8 Mo, a high strength martensitic stainless steel. Although the major fatigue crack which led to specimen failure always occurred at a cylinder-on-flat contact, a crack was often observed at a flat-on-flat site. Significant differences in the early evolution of damage between the two contact configurations were observed.
Full text
Available for:
IJS, IMTLJ, KILJ, KISLJ, NUK, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
PDF
