Splash control of drop impacts with geometric targets

Drop impacts on solid and liquid surfaces exhibit complex dynamics due to the competition of inertial, viscous, and capillary forces. After impact, a liquid lamella develops and expands radially, and under certain conditions, the outer rim breaks up into an irregular arrangement of filaments and secondary droplets. We show experimentally that the lamella expansion and subsequent break up of the outer rim can be controlled by length scales that are of comparable dimension to the impacting drop diameter. Under identical impact parameters, ie. fluid properties and impact velocity, we observe unique splashing dynamics by varying the target cross-sectional geometry. These behaviors include: (i) geometrically-shaped lamellae and (ii) a transition in splashing stability, from regular to irregular splashing. We propose that regular splashes are controlled by the azimuthal perturbations imposed by the target cross-sectional geometry and that irregular splashes are governed by the fastest-growing unstable Plateau-Rayleigh mode

Drop Splashing on a Dry Smooth Surface

The corona splash due to the impact of a liquid drop on a smooth dry substrate is investigated with high speed photography. A striking phenomenon is observed: splashing can be completely suppressed by decreasing the pressure of the surrounding gas. The threshold pressure where a splash first occurs is measured as a function of the impact velocity and found to scale with the molecular weight of the gas and the viscosity of the liquid. Both experimental scaling relations support a model in which compressible effects in the gas are responsible for splashing in liquid solid impacts.Comment: 11 pages, 4 figure

Stromal mesenchyme cell genes of the human prostate and bladder

BACKGROUND: Stromal mesenchyme cells play an important role in epithelial differentiation and likely in cancer as well. Induction of epithelial differentiation is organ-specific, and the genes responsible could be identified through a comparative genomic analysis of the stromal cells from two different organs. These genes might be aberrantly expressed in cancer since cancer could be viewed as due to a defect in stromal signaling. We propose to identify the prostate stromal genes by analysis of differentially expressed genes between prostate and bladder stromal cells, and to examine their expression in prostate cancer. METHODS: Immunohistochemistry using antibodies to cluster designation (CD) cell surface antigens was first used to characterize the stromas of the prostate and bladder. Stromal cells were prepared from either prostate or bladder tissue for cell culture. RNA was isolated from the cultured cells and analyzed by DNA microarrays. Expression of candidate genes in normal prostate and prostate cancer was examined by RT-PCR. RESULTS: The bladder stroma was phenotypically different from that of the prostate. Most notable was the presence of a layer of CD13(+ )cells adjacent to the urothelium. This structural feature was also seen in the mouse bladder. The prostate stroma was uniformly CD13(-). A number of differentially expressed genes between prostate and bladder stromal cells were identified. One prostate gene, proenkephalin (PENK), was of interest because it encodes a hormone. Secreted proteins such as hormones and bioactive peptides are known to mediate cell-cell signaling. Prostate stromal expression of PENK was verified by an antibody raised against a PENK peptide, by RT-PCR analysis of laser-capture microdissected stromal cells, and by database analysis. Gene expression analysis showed that PENK expression was down-regulated in prostate cancer. CONCLUSION: Our findings show that the histologically similar stromas of the prostate and bladder are phenotypically different, and express organ-specific genes. The importance of these genes in epithelial development is suggested by their abnormal expression in cancer. Among the candidates is the hormone PENK and the down-regulation of PENK expression in cancer suggests a possible association with cancer development

Spall And Dynamic Yielding Of Aluminum And Aluminum Alloys At Strain Rates Of 3X10(6) S(-1)

We have explored the role that grain size, impurity particles and alloying in aluminum play in dynamic yielding and spall fracture at tensile strain rates of similar to 3x10(6) We achieved these strain rates shocking the aluminum specimens via laser ablation using the Z-Beamlet Laser at Sandia National Laboratories. The high purity aluminum and 1100 series aluminum alloy produced very different spall strengths and nearly the same yield strengths. In contrast, various grain-sized Al + 3 wt. % Mg specimens presented the lowest spall strength, but the greatest dynamic yield strength. Fracture morphology results and particle analysis are presented along with hydrodynamic simulations to put these results in context. Impurity particles appeared to play a vital role in spall fracture at these fast strain rates. Alloying elements such as Mg seem to be the dominant factor in the dynamic yield results.Mechanical Engineerin

Making a splash with water repellency

A 'splash' is usually heard when a solid body enters water at large velocity. This phenomena originates from the formation of an air cavity resulting from the complex transient dynamics of the free interface during the impact. The classical picture of impacts on free surfaces relies solely on fluid inertia, arguing that surface properties and viscous effects are negligible at sufficiently large velocities. In strong contrast to this large-scale hydrodynamic viewpoint, we demonstrate in this study that the wettability of the impacting body is a key factor in determining the degree of splashing. This unexpected result is illustrated in Fig.1: a large cavity is evident for an impacting hydrophobic sphere (1.b), contrasting with the hydrophilic sphere's impact under the very same conditions (1.a). This unforeseen fact is furthermore embodied in the dependence of the threshold velocity for air entrainment on the contact angle of the impacting body, as well as on the ratio between the surface tension and fluid viscosity, thereby defining a critical capillary velocity. As a paradigm, we show that superhydrophobic impacters make a big 'splash' for any impact velocity. This novel understanding provides a new perspective for impacts on free surfaces, and reveals that modifications of the detailed nature of the surface -- involving physico-chemical aspects at the nanometric scales -- provide an efficient and versatile strategy for controlling the water entry of solid bodies at high velocity.Comment: accepted for publication in Nature Physic

Development, Refinement, and Psychometric Properties of the Attitudes Toward God Scale (ATGS-9)

Perceived relationships with God can be a source of comfort or struggle. To advance the study of spiritual comfort and struggle, we develop the nine-item Attitudes toward God Scale (ATGS-9), and we describe six studies (2,992 total participants) reporting its development and psychometrics. Exploratory and confirmatory factor analyses identified two factors: (1) Positive Attitudes toward God and (2) Disappointment and Anger with God. Subscale scores showed good estimated internal consistency, 2-week temporal stability, and evidence for construct and discriminant validity. Positive Attitudes toward God correlated with measures of religiosity and conscientiousness. Disappointment and Anger with God correlated with negative religious coping, lower religious participation, more distress, higher neuroticism, and entitlement. These results support the ATGS-9 as a brief measure of attitudes toward God

Defining forgiveness: Christian clergy and general population perspectives.

The lack of any consensual definition of forgiveness is a serious weakness in the research literature (McCullough, Pargament &amp; Thoresen, 2000). As forgiveness is at the core of Christianity, this study returns to the Christian source of the concept to explore the meaning of forgiveness for practicing Christian clergy. Comparisons are made with a general population sample and social science definitions of forgiveness to ensure that a shared meaning of forgiveness is articulated. Anglican and Roman Catholic clergy (N = 209) and a general population sample (N = 159) completed a postal questionnaire about forgiveness. There is agreement on the existence of individual differences in forgiveness. Clergy and the general population perceive reconciliation as necessary for forgiveness while there is no consensus within psychology. The clergy suggests that forgiveness is limitless and that repentance is unnecessary while the general population suggests that there are limits and that repentance is necessary. Psychological definitions do not conceptualize repentance as necessary for forgiveness and the question of limits has not been addressed although within therapy the implicit assumption is that forgiveness is limitless.</p