Search results for "Isolation"

Sapropeļa kūdras, sapropeļa kokskaidu siltumizolācijas plāksnes un to īpašības

2014

Siltumizolācijas materiāli, kuros par pildvielu tiktu izmantoti vietējie biomasas produkti, bet par saistvielu kalpotu dabiskas izcelsmes saistvielas, piemēram, sapropelis, uzskatāmi par inovatīviem un to pielietošana sekmētu ekoloģiskās būvniecības nozares attīstību. Šādu risinājumu izstrāde ir aktuāla, jo Latvijā ir ievērojami sapropeļa resursi, kuru izmantošanu kavē to nepietiekama izpēte un ekoloģiskās būvniecības nozares intensīva attīstība. Pētījuma mērķis ir iegūt sapropeļa-koksnes, kūdras-koksnes siltumizolācijas plāksnes, noteikt optimālās plātnes sastāva attiecības un raksturot iegūto plātņu īpašības. Veikto pētījumu rezultātā tika noteiktas siltumizolācijas materiālu paraugu mehā…

Exploring the experiences of being an ethnic minority student within undergraduate nurse education: a qualitative study

2019

Abstract Background Students studying in a country where another language is spoken face multiple challenges including their ability to fully integrate with peers and academic pressures in trying to obtain an undergraduate nursing degree. The aim of the study was to explore the lived experiences of students, from varying cultural and ethnic backgrounds, undertaking an undergraduate nursing degree. Methods The study adopted a qualitative design and eight individual semi-structured interviews were conducted. The interviews were analysed using manifest content analysis according to Graneheim and Lundman. Results Students reported feelings of isolation and the lack of opportunities to integrate…

Evolution of Complex Acoustic Signals in Drosophila Species

2009

species produce complex acous-tic cues, so-called courtship songs, while pursuing a female.In most of the over 100 species studied so far (see thelist of these species in Hoikkala, 2005), such cues areproduced by wing vibration. Other mechanisms of songproduction include abdomen purring (Hoy, Hoikkala, &Kaneshiro, 1988) and rapid vibrations of the whole body(Ritchie & Gleason, 1995). The carrier frequency of songsproduced through any of these actions ranges from 150 to500Hz. A hitherto unknown mechanism enables males ofsome Hawaiian species to generate songs of up to 15,000Hz(Hoikkala, Hoy, & Kaneshiro, 1989).The structure of the courtship songs of closely relatedspecies often reflects phylo…

2014

The free-living planktonic freshwater bacterium Polynucleobacter necessarius subspecies asymbioticus (> 99% 16S rRNA similarity) represents a taxon with a cosmopolitan distribution and apparently ubiquitous occurrence in lentic freshwater habitats. We tested for intra-taxon biogeographic patterns by combining cultivation-independent and cultivation methods. A culture collection of 204 strains isolated from globally distributed freshwater habitats (Arctic to Antarctica) was investigated for phylogeographic patterns based on sequences of two markers, the 16S–23S internal transcribed spacers and the glutamine synthetase gene (glnA). Genetic distance between isolates showed significant geograph…

Dispersal history of a spider (Stegodyphus lineatus) across contiguous deserts: vicariance and range expansion

2005

Israel marks a crossroads between three continents encompassing several phytogeographical and zoogeographical zones. In this complex area, the flow of species from different biogeographical regions creates opportunities to study how geographical division and colonization routes affect current distribution and structure of resident populations of organisms associated with desert and arid environments, habitats that may have persisted throughout Pleistocene glacial periods. The present paper analyses the population history of the spider Stegodyphus lineatus in the contiguous Negev and Judean deserts in Israel using allozyme and mtDNA variation. The distinct patterns of variation indicate that…

International Retirement Migration: Transforming Societies Through Purchasing Power?

2016

Despite a more than 40-year-old tradition of international retirement migration (IRM) in Europe, relatively little social scientific research has been carried out in this field. Retired European migrants have not been considered to be politically controversial (i.e. they are not viewed as having been the causes of social problems or as needy, poor or deprived). Often, the terms used in the 1980s and early 1990s to describe these populations have been linked not to a migration model but to the model of the social agent of a tourist. The chapter is divided into three parts: (1) a general overview of the flows and socio-economic characteristics of IRM in Europe, addressing the main regions of …

Analysis of gene flow and habitat patch network for Chazara briseis (Lepidoptera: Satyridae) in an agricultural landscape

1997

Abstract A fine geographic-scale population genetic structure analysis was performed for the endangered butterfly species Chazara briseis in the region of Halle an der Saale, Germany, for the investigation of gene flow and possible effects of habitat fragmentation on genetic variability. Patterns of genetic variance were estimated by allozyme electrophoresis and quantified with F -statistics. Levels of genetic variation were high, expected heterozygosity H e = 0.20, and mean number of alleles per locus, A = 1.93, indicating large population sizes. Butterflies inhabiting the study area probably constituted just one population and the fragmented nature of the habitat patches did not substanti…

Allozyme variation in populations of scallops, Pecten jacobaeus (L.) and P. maximus (L.) (Bivalvia: Pectinidae), across the Almeria–Oran front

2002

Abstract The scallops Pecten jacobaeus and P. maximus have been traditionally considered as different species which shared a common ancestor some 5 Ma ago. This view has been challenged by recent reports of genetic distances based on allozymes and mitochondrial DNA which are incompatible with such a long period of isolation and are more typical of conspecific populations. To explain the slight allozyme differentiation opposed to a clear morphological distinctiveness, two main hypotheses have been proposed. One hypothesis views interpopulation allozyme differentiation as an outcome of simple population genetic processes such isolation by distance. The other considers that the intertaxa alloz…

Mate recognition as a reproductive barrier in sexual and parthenogenetic Eucypris virens (Crustacea, Ostracoda)

2013

Mate selection is one of the motors of evolution and of particular importance in the case of organisms in which sexual and parthenogenetic populations coexist. Sexual populations of the ostracod species complex Eucypris virens are often mixed with parthenogenetic ones. A powerful mate selection mechanism must exist to avoid time, energy and sperm loss, for the maintenance and success of sexual reproduction in these mixed populations. There are four types of E. virens individuals: males (diploid), sexual females (diploid) and asexual females (parthenogenetic and either di- or triploid). From one parthenogenetic population and two populations with males of E. virens, we sampled early stage ju…

The effectiveness of pre- and post-zygotic barriers in avoiding hybridization between two snapdragons (Antirrhinum L.: Plantaginaceae)

2014

Reproductive barriers play an important role in the maintenance of species boundaries. However, to date, few studies have provided a detailed analysis of reproductive isolation barriers between species or examined their importance in maintaining species identity. This is the first detailed study into pre- and post-zygotic reproductive isolation barriers in Antirrhinum, based on a mixed population with two species that rarely co-occur. The study revealed that pollinator constancy and preference and poor hybrid seed viability were the most important reproductive isolating mechanisms. Reproductive isolation was practically complete by both pre- and post-zygotic barriers. Average pre-zygotic is…