Enhancing the bandwidth of piezoelectric composite transducers for air-coupled non-destructive evaluation

This paper details the development of a novel method for increasing the operational bandwidth of piezocomposites without the need for lossy backing material, the aim being to increase fractional bandwith by geometrical design. Removing the need for lossy backing materials, should in turn increase the transmit efficiency in the desired direction of propagation. Finite element analysis has been employed to determine the mode of operation of the new piezocomposite devices and shows good correlation with that derived experimentally. Through a series of practical and analytical methods it has been shown that additional thickness mode resonances can be introduced into the structure by a simple machining process. The shaped composites described in this paper offer increased operational bandwidth. A simple example of a two step thickness design is described to validate and illustrate the principle. A more complex conical design is presented that illustrates a possible tenfold increase in bandwidth from 30kHz to 300kHz, operating in air without backing. An illustration of the applicability of this type of transducer technology for frequency agile guided mode non-destructive evaluation is then presented

Two Dimensional Anti-de Sitter Space and Discrete Light Cone Quantization

We realize the two dimensional anti-de Sitter ($AdS_2$) space as a Kaluza-Klein reduction of the $AdS_3$ space in the framework of the discrete light cone quantization (DLCQ). Introducing DLCQ coordinates which interpolate the original (unboosted) coordinates and the light cone coordinates, we discuss that $AdS_2/CFT$ correspondence can be deduced from the $AdS_3/CFT$. In particular, we elaborate on the deformation of WZW model to obtain the boundary theory for the $AdS_2$ black hole. This enables us to derive the entropy of the $AdS_2$ black hole from that of the $AdS_3$ black hole.Comment: RevTeX, 11 pages, shorter version to appear in PL

Ageing, income and living standards: evidence from the British Household Panel Survey

ABSTRACTIn Britain, older people have lower average incomes and a higher risk of income poverty than the general population. Older pensioners are more likely to be in poverty than younger ones. Yet certain indicators of their living standards suggest that older people experience less hardship than expected, given their incomes. A possible explanation is that older people convert income into basic living standards at a higher rate than younger people, implying that as people age they need less income to achieve a given standard of living. Much existing evidence has been based on cross-sectional data and therefore may not be a good guide to the consequences of ageing. We use longitudinal data on people aged at least 50 years from the British Household Panel Survey to investigate the effects of ageing on the relationship between standard of living, as measured by various deprivation indices, and income. We find that for most indices, ageing increases deprivation when controlling for income and other factors. The exception is a subjective index of , which appears to fall as people age. We also find evidence of cohort effects. At any given age and income, more-recently-born older people in general experience more deprivation than those born longer ago. To some extent these ageing and cohort effects balance out, which suggests that pensions do not need to change with age

An Approach to the Cosmological Constant Problem(s)

We propose an approach to explaining why naive large quantum fluctuations are not the right estimate for the cosmological constant. We argue that the universe is in a superposition of many vacua, in such a way that the resulting fluctuations are suppressed by level repulsion to a very small value. The approach combines several aspects of string theory and the early history of the universe, and is only valid if several assumptions hold true. The approach may also explain why the effective cosmological constant reamins small as the universe evolves though several phase transitions. It provides a non-anthropic mechansim leading to a small, non-zero cosmological constant.Comment: Talk given at Rencontres de Moriond, 2004 by G.L. Kan

Three Dimensional Gauge Theories and Monopoles

The coulomb branch of $N=4$ supersymmetric Yang-Mills gauge theories in $d=2+1$ is studied. A direct connection between gauge theories and monopole moduli spaces is presented. It is proposed that the hyper-K\"ahler metric of supersymmetric $N=4$ $SU(N)$ Yang-Mills theory is given by the charge $N$ centered moduli space of BPS monopoles in $SU(2)$. The theory is compared to $N=2$ supersymmetric Yang-Mills theory in four dimensions through compactification on a circle of the latter. It is found that rational maps are appropriate to this comparison. A BPS mass formula is also written for particles in three dimensions and strings in four dimensions.Comment: 25 page

The Discovery of XY Sex Chromosomes in a \u3cem\u3eBoa\u3c/em\u3e and \u3cem\u3ePython\u3c/em\u3e

For over 50 years, biologists have accepted that all extant snakes share the same ZW sex chromosomes derived from a common ancestor [1, 2, 3], with different species exhibiting sex chromosomes at varying stages of differentiation. Accordingly, snakes have been a well-studied model for sex chromosome evolution in animals [1, 4]. A review of the literature, however, reveals no compelling support that boas and pythons possess ZW sex chromosomes [2, 5]. Furthermore, phylogenetic patterns of facultative parthenogenesis in snakes and a sex-linked color mutation in the ball python (Python regius) are best explained by boas and pythons possessing an XY sex chromosome system [6, 7]. Here we demonstrate that a boa (Boa imperator) and python (Python bivittatus) indeed possess XY sex chromosomes, based on the discovery of male-specific genetic markers in both species. We use these markers, along with transcriptomic and genomic data, to identify distinct sex chromosomes in boas and pythons, demonstrating that XY systems evolved independently in each lineage. This discovery highlights the dynamic evolution of vertebrate sex chromosomes and further enhances the value of snakes as a model for studying sex chromosome evolution

Creating correct aberrations: why blur isn’t always bad in the eye

In optics in general, a sharp aberration-free image is normally the desired goal, and the whole field of adaptive optics has developed with the aim of producing blur-free images. Likewise, in ophthalmic optics we normally aim for a sharp image on the retina. But even with an emmetropic, or well-corrected eye, chromatic and high order aberrations affect the image. We describe two different areas where it is important to take these effects into account and why creating blur correctly via rendering can be advantageous. Firstly we show how rendering chromatic aberration correctly can drive accommodation in the eye and secondly report on matching defocus-l generated using rendering with conventional optical defocus

Probiotics to prevent infantile colic

Background Infantile colic is typically defined as full‐force crying for at least three hours per day, on at least three days per week, for at least three weeks. Infantile colic affects a large number of infants and their families worldwide. Its symptoms are broad and general, and while not indicative of disease, may represent a serious underlying condition in a small percentage of infants who may need a medical assessment. Probiotics are live microorganisms that alter the microflora of the host and provide beneficial health effects. The most common probiotics used are of Lactobacillus, Bifidobacterium and Streptococcus. There is growing evidence to suggest that intestinal flora in colicky infants differ from those in healthy infants, and it is suggested that probiotics can redress this balance and provide a healthier intestinal microbiota landscape. The low cost and easy availability of probiotics makes them a potential prophylactic solution to reduce the incidence and prevalence of infantile colic. Objectives To evaluate the efficacy and safety of prophylactic probiotics in preventing or reducing severity of infantile colic. Search methods In January 2018 we searched CENTRAL, MEDLINE, Embase, PsycINFO, CINAHL, 10 other databases and two trials registers. In addition, we handsearched the abstracts of relevant meetings, searched reference lists, ran citation searches of included studies, and contacted authors and experts in the field, including the manufacturers of probiotics, to identify unpublished trials. Selection criteria Randomised control trials (RCTs) of newborn infants less than one month of age without the diagnosis of infantile colic at recruitment. We included any probiotic, alone or in combination with a prebiotic (also known as synbiotics), versus no intervention, another intervention(s) or placebo, where the focus of the study was the effect of the intervention on infantile colic. Data collection and analysis We used standard methodological procedures of Cochrane. Main results Our search yielded 3284 records, and of these, we selected 21 reports for full‐text review. Six studies with 1886 participants met our inclusion criteria, comparing probiotics with placebo. Two studies examined Lactobacillus reuteri DSM, two examined multi‐strain probiotics, one examined Lactobacillus rhamnosus, and one examined Lactobacillus paracasei and Bifidobacterium animalis. Two studies began probiotics during pregnancy and continued administering them to the baby after birth. We considered the risk of bias for randomisation as low for all six trials; for allocation concealment as low in two studies and unclear in four others. All studies were blinded, and at low risk of attrition and reporting bias. A random‐effects meta‐analysis of three studies (1148 participants) found no difference between the groups in relation to occurrence of new cases of colic: risk ratio (RR) 0.46, 95% confidence interval (CI) 0.18 to 1.19; low‐certainty evidence; I2 = 72%. A random‐effects meta‐analysis of all six studies (1851 participants) found no difference between the groups in relation to serious adverse effects (RR 1.02, 95% CI 0.14 to 7.21; low‐certainty evidence; I2 not calculable (only four serious events for one comparison, two in each group: meconium plug obstruction, patent ductus arteriosus and neonatal hepatitis). A random‐effects meta‐analysis of three studies (707 participants) found a mean difference (MD) of –32.57 minutes per day (95% CI –55.60 to –9.54; low‐certainty evidence; I2 = 93%) in crying time at study end in favour of probiotics. A subgroup analysis of the most studied agent, Lactobacillus reuteri, showed a reduction of 44.26 minutes in daily crying with a random‐effects model (95% CI –66.6 to –21.9; I2 = 92%), in favour of probiotics. Authors' conclusions There is no clear evidence that probiotics are more effective than placebo at preventing infantile colic; however, daily crying time appeared to reduce with probiotic use compared to placebo. There were no clear differences in adverse effects. We are limited in our ability to draw conclusions by the certainty of the evidence, which we assessed as being low across all three outcomes, meaning that we are not confident that these results would not change with the addition of further researc