Gradient of Tactile Properties in the Rat Whisker Pad

The array of vibrissae on a rat’s face is the first stage in a high-resolution tactile sensing system. Progressing from rostral to caudal in any vibrissae row results in an increase in whisker length and thickness. This in turn may provide a systematic map of separate tactile channels governed by the mechanical properties of the whiskers. To examine whether this map is expressed in a location-dependent transformation of tactile signals into whisker vibrations and neuronal responses, we monitored whiskers’ movements across various surfaces and edges. We found a robust rostral-caudal gradient of tactile information transmission in which rostral shorter vibrissae displayed a higher sensitivity and a bigger differences in response to the different textures, whereas longer caudal vibrissae were less sensitive to the different textures. Nonetheless, we found that texture identity is not represented spatially across the whisker pad. Based on the responses of first-order sensory neurons, we found that neurons innervating rostral whiskers were better suited for textures discrimination, whereas neurons innervating caudal whiskers were more suited for edge detection. To examine the functional role of this organization, we monitored the whisking activity of awake rats foraging for food. We found a caudal-rostral gradient of whisking angle movements in which the longer caudal vibrissae spanned a larger space making them more suitable for object localization, whereas the rostral shorter vibrissae hardly moved. These results suggest that the whisker array in rodents forms a sensory structure in which different facets of tactile information are transmitted through location-dependent gradient of vibrissae on the rat’s face.

Layer 4 barrel cortex neurons retain their response properties during whisker replacement

Bodies change continuously, but we do not know if and how these changes affect somatosensory cortex. We address this issue in the whisker-barrel-cortex-pathway. We ask how outgrowing whiskers are mapped onto layer 4 barrel neuron responses. Half of whisker follicles contained dual whiskers, a shorter presumably outgrowing whisker (referred to as young whisker) and a longer one (referred to as old whisker). Young whiskers were much thinner than old ones but were inserted more deeply into the whisker follicle. Both whiskers were embedded in one outer root sheath surrounded by a common set of afferent nerve fibers. We juxtacellularly identified layer 4 barrel neurons representing dual whiskers with variable whisker length differences in anesthetized rats. Strength and latency of neuronal responses were strongly correlated for deflections of young and old whiskers but were not correlated with whisker length. The direction preferences of young and old whiskers were more similar than expected by chance. Old whiskers evoked marginally stronger and slightly shorter latency spike and local field potential responses than young whiskers. Our data suggest a conservative rewiring mechanism, which connects young whiskers to existing peripheral sensors. The fact that layer 4 barrel neurons retain their response properties is remarkable given the different length, thickness, and insertion depth of young and old whiskers. Retention of cortical response properties might be related to the placement of young and old whisker in one common outer root sheath and may contribute to perceptual stability across whisker replacement. NEW & NOTEWORTHY A particularly dramatic bodily change is whisker regrowth, which involves the formation of dual whisker follicles. Our results suggest that both whiskers are part of the same mechanoreceptive unit. Despite their distinct whisker length and thickness, responses of single cortical neurons to young and old whisker deflection were similar in strength, latency, and directional tuning. We suggest the congruence of young and old whisker cortical responses contributes to perceptual stability over whisker regrowth.

An investigation of tin whisker growth over a 32-year period

Purpose This paper aims to present the results of a 32-year-old laboratory study of whisker growth from tin electrodeposits that was originally undertaken to gain an increased understanding of the phenomenon of tin whisker growth. Design/methodology/approach Whisker growth was evaluated using electroplated C-rings (both stressed and un-stressed) that were stored throughout in a desiccator at room temperature. Analysis has recently been undertaken to evaluate whisker growth and intermetallic growth after 32 years of storage. Scanning electron microscopy analysis has been performed to investigate whisker length and, using polished cross-sections, the morphology, thickness and type of intermetallic formation. Findings Normal tin-plated deposits on brass and steel with a copper barrier layer nucleated whiskers within five months, and in each case, these grew to lengths between 1 and 4.5 mm. For normal tin electroplated onto brass, a one- or two-month nucleation period was needed before whiskers developed. They reached a maximum length of about 1.5 mm after six months, and little or no further growth occurred during the subsequent 32 years. Very few whiskers grew on the tin-plated steel samples and no intermetallic formation was observed. None of the fused tin plating samples nucleated whiskers during the 32-year period. Practical implications Knowledge about vintage whiskers is important to take steps to increase the resiliency of space missions. Similarly, such knowledge is important to engineers engaged in products reaching their nominal end-of-life, but where, for reasons of economy, these products cannot be replaced. Originality/value This study represents a unique insight into whisker growth and intermetallic formation over an extremely long time period.

The Effects of Nickel Underlayer and Solder Dipping as Tin Whisker Mitigations in Tin Surface Finishes

Driven by environmental concerns and the enforcement of Restriction of Hazardous Substances Directive (RoHS) to ban the use of lead in electronics, the global electronics industry has migrated toward lead-free electronics. However, the adoption of lead-free tin (Sn) surface finish is known to form whiskers. These whiskers grow spontaneously from the Sn finish layer as a stress-relief over time causing device failures. In the present research, whisker growth is investigated via immersion Sn finishes on Cu substrate. The effects of Sn layer thickness, addition of Ni under-layer and solder dipping on whisker growth are investigated by storing the samples under ambient temperature for up to 24 weeks. The effects of external stresses were also studied using bending test. The results showed that whisker length on immersion Sn increases with time for all the samples either with or without Ni under-layer. Thicker Sn coating showed more whisker growth compared with thinner Sn coating. The longest whisker length of 23μm was observed for Sn coating with 2μm thickness. The addition of Ni as under-layer was found to be more effective in mitigating the whisker growth by extending the incubation time for whisker formation. Compared to immersion Sn, solder dipping in pure Sn showed no whisker growth. However, alloying Sn with 0.4%wtCu resulted in whisker growth indicating the role of Cu in promoting whiskers formation.

Study on Synthesis of the High Aspect Ratios Nesquehonite Whiskers

In this paper, nesquehonite whiskers were synthesized by low-temperature aqueous solution method, and the impacts of reaction temperature, reaction time and surfactant dosage and other factors on the maximum whisker length and high aspect ratios of nesquehonite whiskers were also investigated. Results showed that under the conditions that the reaction temperature was 40 – 50 °C the reaction time was 50 – 60min and the amount of surfactant dosage was 1% (by mass), high aspect ratios nesquehonite whisker products can be synthesized. On this basis, growth mechanism of the nesquehonite whiskers was discussed.

PART 3 New Experiments Three Factors On The Box plot, Box notch & Outlier Values

New two experiments of the three factors, in this study were constructed to investigate the effects, of the fixed variations to the box plot on subjects' judgments of the box lengths. These two experiments were constructed as an extension to the group B experiments, the ratio experiments the experiments with two variables carried out previously by Hussin, M.M. (1989, 2006, 2007). The first experiment box notch experiment, and the second experiment outlier values experiment. Subjects were asked to judge what percentage the shorter represented of the longer length in pairs of box lengths and give an estimate of percentage, one being a standard plot and the other being of a different box lengths and also varying with respect to other elements such as, box width & box notch or box width & outlier values. When Hussin, M.M. (1989) suggested in the future research points (1, 2, 3), can take account of wider range of the variables levels and the changing length of the standard box plot effects on the subjects' perception of the box length and further investigations could be made into variations such as box notch with box length; box notch with box length; whisker length, and also outlier values with these variations. However, both experiments were used the stander box length as the middle box length levels were not used in the experiments. The results of these two experiments suggest that these variations effected the subjects' perception of box length, as a results of the interactions between box plot features by creating visual illusions as which effect the subjects ability to accurately judge box length, both experiments were run in statistics department, Baghdad University.

PART 2 An Experiment on the Box plot

These experiments seek to investigate the effects of the fixed variations to the basic box plot on subjects' judgments of the box lengths. The study consists of two experiments, were constructed as an extension to the experiments carried out previously by Hussin, M.M. (1989, 2006). Subjects were asked to judge what percentage the shorter represented of the longer length in pairs of box lengths and give an estimate of percentage, one being a standard plot and the other being of a different box length and also varying with respect to other elements such as, box width or whisker length. When he (1989) suggested in the future research points (1, 2), the changing length of the standard box plot effects on the subjects' perception of the box length. However, both experiments were used the stander box length as the middle box length levels in the experiments. The results of these two experiments indicated that these variations effected the subjects' perception of box length. we thought that the effect in the subjects perception of these variations it might be that the subjects were affected by the visual illusion effects as Cleveland et al (1987) accepted in their replies to the comments on their work, as a results of the interactions between box plot features as which effect the subjects ability to accurately judge box length and the effects differed between variations, both experiments were run in statistics department, Baghdad University.

Shape-Controlled Synthesis of Hydroxyapatite in Organic Media

We have examined the effect of organic solvent on the microstructures of hydroxyapatite (HAp) formed by hydrolysis of α -tricalcium phosphate ( α -TCP) in heterogeneous solvent system (water-hydrophobic organic solvent). The shape of HAp was like ultrafine whisker (length : about 1 ∼- 4 µ m) and its size depended on the used organic solvent.As a simple hybridization, incorporation of fluoride anion (F−) into HAp was attempted in similar system to obtain fluoridated apatite [Ca10(PO4)6(OH)2−x Fx.]. The formation rate was strongly affected by the concentration of F− and reaction temperature. Although the product in water (in the absence of organic solvent) consists of fine particles less than 1 µ m, the product prepared in the heterogeneous solvent system was mixture of ultrafine particles ( ∼ 0.1 µ m) and needle-like particles (length : about 1 ∼ 4 µ m, width : ∼ 0.5 µ m). The microstructures of HAp and FHAp were controlled by hydrophobicity of organic solvent.

The Effects of Display Characteristics on the Bias of Estimates of Whisker Length of Regular and Notched Boxplots

This study investigated the effects of display characteristics on the bias of estimates of whisker length of two different types of box-and-whisker plots. To test the hypothesis that the bias means of estimates of whisker length were significantly different for the experimental and control groups, a 2.234 mixed design was utilized. Notched box-and-whisker plots and regular box-and-whisker plots were levels of the between-subjects factor, while within-subjects factors were the interquartile spread, whisker length, and spatial orientation of the graphs. Results indicate that although there was no significant difference in the bias means associated with the two types of plots, bias seems to be the product of a three-way interaction between spatial orientation, interquartile spread, and whisker/spread ratio.