University of St Andrews

About: University of St Andrews is a education organization based out in St Andrews, Fife, United Kingdom. It is known for research contribution in the topics: Population & Laser. The organization has 16260 authors who have published 43364 publications receiving 1636072 citations. The organization is also known as: St Andrews University & University of St. Andrews.

Optical tweezers and optical spanners with Laguerre-Gaussian modes

Abstract: We numerically model the axial trapping forces within optical tweezers arising from Laguerre–Gaussian laser modes. For an 8 μm diameter sphere suspended in water, the higher-order modes produce an axial trapping force several times larger than that of the fundamental. Partial absorption results in a transfer of the orbital angular momentum from the Laguerre–Gaussian mode to the trapped particle. This results in the rotation of the particle by what may be called an optical spanner (wrench). For an absorption coefficient of α = 5700 m−1 and a laser power of 10 mW, we find that an 8 μm diameter sphere would acquire an angular acceleration of 10 × 104 rad s−2 and a limiting angular velocity of 0.2 rad s−1.

Latitudinal variation in the abundance and oxidative capacities of muscle mitochondria in perciform fishes

Abstract: The abundance, distribution and oxidative capacities of mitochondria have been investigated in the red pectoral fin adductor muscles of fish (Order Perciformes) that use a predominantly labriform style of swimming. Mediterranean Sea species from the families Labridae, Serranidae, Sparidae and Antarctic Nototheniidae and non-Antarctic Nototheniidae and Channichthyidae were studied. Sub-Antarctic species from the Beagle Channel, Tierra del Fuego, included the pelagic haemoglobin-less icefish (Champsocephalus esox) and the robalo (Eleginops maclovinus), which occurs as far north as 35 degrees S. In Champsocephalus esox, the mitochondrial volume density of red muscle was 0.51 and mitochondrial cristae surface density (43. 9 microm2 microm-3) was higher than reported for Antarctic icefishes. In the red-blooded, active pelagic or semi-pelagic species, mitochondrial volume density was within the range 0.27-0.33 regardless of habitat temperature. Amongst less active demersal species, mitochondrial volume density ranged from 0.29-0.33 in polar species to 0.08-0.13 in Mediterranean species. In Antarctic species and Champsocephalus esox, myofibrils occurred in ribbons or clusters one fibril thick entirely surrounded by mitochondria. The volume density of intracellular lipid droplets was not correlated with activity patterns or habitat temperature. In a comparison of Eleginops maclovinus caught in summer (approximately 10 degrees C) and winter (approximately 4 degrees C), mitochondrial volume density did not differ, whereas the surface density of mitochondrial clusters was higher in summer fish. The temperature-dependence of the state 3 respiration rate of isolated mitochondria with pyruvate as substrate was described by a single quadratic relationship for all species, indicating no significant up-regulation of the maximum rate of oxygen uptake per milligram mitochondrial protein in Antarctic species. Our results support the conclusion that increasing the volume and surface density of mitochondrial clusters is the primary mechanism for enhancing the aerobic capacity of muscle in cold-water fish.

Wave propagation in a magnetically structured atmosphere

Abstract: The solar atmosphere, from the photosphere to the corona, is structured by the presence of magnetic fields. We consider the nature of such inhomogeneity and emphasis that the usual picture of hydromagnetic wave propagation in a uniform medium may be misleading if applied to a structured field. We investigate the occurrence of magnetoacoustic surface waves at a single magnetic interface and consider in detail the case where one side of the interface is field-free. For such an interface, a slow surface wave can always propagate. In addition, a fast surface wave may propagate if the field-free medium is warmer than the magnetic atmosphere.

The ADOR Mechanism for the Synthesis of New Zeolites

Abstract: A novel methodology, called ADOR (assembly–disassembly–organisation–reassembly), for the synthesis of zeolites is reviewed here in detail. The ADOR mechanism stems from the fact that certain chemical weakness against a stimulus may be present in a zeolite framework, which can then be utilized for the preparation of new solids through successive manipulation of the material. In this review, we discuss the critical factors of germanosilicate zeolites required for application of the ADOR protocol and describe the mechanism of hydrolysis, organisation and condensation to form new zeolites starting from zeolite UTL. Last but not least, we discuss the potential of this methodology to form other zeolites and the prospects for future investigations.

The relation between the most-massive star and its parental star cluster mass

Abstract: We present a thorough literature study of the most-massive star, mmax, in several young star clusters in order to assess whether or not star clusters are populated from the stellar initial mass function (IMF) by random sampling over the mass range 0.01 6 m 6 150 M⊙ without being constrained by the cluster mass, Mecl. The data reveal a partition of the sample into lowest mass objects (Mecl 6 10 2 M⊙), moderate mass clusters (10 2 M⊙ < Mecl 6 10 3 M⊙) and rich clusters above 10 3 M⊙. Additionally, there is a plateau of a constant maximal star mass (mmax � 25 M⊙) for clusters with masses between 10 3 M⊙ and 4 · 10 3 M⊙. Statistical tests of this data set reveal that the hypothesis of random sampling from the IMF between 0.01 and 150 M⊙ is highly unlikely for star clusters more massive than 10 2 M⊙ with a probability of p � 2· 10 −7 for the objects with Mecl between 10 2 M⊙ and 10 3 M⊙ and p � 3 · 10 −9 for the more massive star clusters. Also, the spread of mmax values at a given Mecl is smaller than expected from random sampling. We suggest that the basic physical process able to explain this dependence of stellar inventory of a star cluster on its mass may be the interplay between stellar feedback and the binding energy of the cluster-forming molecular cloud core. Given these results, it would follow that an integrated galactic initial mass function (IGIMF) sampled from such clusters would automatically be steeper in comparison to the IMF within individual star clusters.