Ohm's Law Survives to the Atomic Scale Weber, B.; Mahapatra, S.; Ryu, H. ...
Science (American Association for the Advancement of Science),
01/2012, Letnik:
335, Številka:
6064
Journal Article
Recenzirano
As silicon electronics approaches the atomic scale, interconnects and circuitry become comparable in size to the active device components. Maintaining low electrical resistivity at this scale is ...challenging because of the presence of confining surfaces and interfaces. We report on the fabrication of wires in silicon—only one atom tall and four atoms wide—with exceptionally low resistivity (~0.3 milliohm-centimeters) and the current-carrying capabilities of copper. By embedding phosphorus atoms within a silicon crystal with an average spacing of less than 1 nanometer, we achieved a diameter-independent resistivity, which demonstrates ohmic scaling to the atomic limit. Atomistic tight-binding calculations confirm the metallicity of these atomic-scale wires, which pave the way for single-atom device architectures for both classical and quantum information processing.
Populations distributed across a broad thermal cline are instrumental in addressing adaptation to increasing temperatures under global warming. Using a space‐for‐time substitution design, we tested ...for parallel adaptation to warm temperatures along two independent thermal clines in Zostera marina, the most widely distributed seagrass in the temperate Northern Hemisphere. A North–South pair of populations was sampled along the European and North American coasts and exposed to a simulated heatwave in a common‐garden mesocosm. Transcriptomic responses under control, heat stress and recovery were recorded in 99 RNAseq libraries with ~13 000 uniquely annotated, expressed genes. We corrected for phylogenetic differentiation among populations to discriminate neutral from adaptive differentiation. The two southern populations recovered faster from heat stress and showed parallel transcriptomic differentiation, as compared with northern populations. Among 2389 differentially expressed genes, 21 exceeded neutral expectations and were likely involved in parallel adaptation to warm temperatures. However, the strongest differentiation following phylogenetic correction was between the three Atlantic populations and the Mediterranean population with 128 of 4711 differentially expressed genes exceeding neutral expectations. Although adaptation to warm temperatures is expected to reduce sensitivity to heatwaves, the continued resistance of seagrass to further anthropogenic stresses may be impaired by heat‐induced downregulation of genes related to photosynthesis, pathogen defence and stress tolerance.
An evolutionary epigenetic clock in plants Yao, N.; Zhang, Z.; Yu, L. ...
Science (American Association for the Advancement of Science),
09/2023, Letnik:
381, Številka:
6665
Journal Article
Recenzirano
Odprti dostop
Molecular clocks are the basis for dating the divergence between lineages over macroevolutionary timescales (~10
5
to 10
8
years). However, classical DNA-based clocks tick too slowly to inform us ...about the recent past. Here, we demonstrate that stochastic DNA methylation changes at a subset of cytosines in plant genomes display a clocklike behavior. This “epimutation clock” is orders of magnitude faster than DNA-based clocks and enables phylogenetic explorations on a scale of years to centuries. We show experimentally that epimutation clocks recapitulate known topologies and branching times of intraspecies phylogenetic trees in the self-fertilizing plant
Arabidopsis thaliana
and the clonal seagrass
Zostera marina
, which represent two major modes of plant reproduction. This discovery will open new possibilities for high-resolution temporal studies of plant biodiversity.
Editor’s summary
Molecular clocks provide the basis for many population genetic and evolutionary inferences, but are limited in use for recent generations because of low germline mutation rates. In plants, heritable changes in epigenetic markers, known as epimutations, occur at higher rates than genetic mutations. Yao
et al
. were able to develop a tool that allows for the estimation of phylogenies based on these epimutations (see the Perspective by Satyaki). The authors located regions of the genome that experience neutral, clock-like epimutations in the classic plant model
Arabidopsis thaliana
and were able to recapitulate known phylogenies of very recent time scales. This study will help to provide the tools and theoretical basis for estimating recent phylogenies in many plant species. —Corinne Simonti
A fast-ticking evolutionary epigenetic clock in plants facilitates phylogenetic insights into the recent past.
Nanoscale control of doping profiles in semiconductor devices is becoming of critical importance as channel length and pitch in metal oxide semiconductor field effect transistors (MOSFETs) continue ...to shrink toward a few nanometers. , Scanning tunneling microscope (STM) directed self-assembly of dopants is currently the only proven method for fabricating atomically precise electronic devices in silicon. To date this technology has realized individual components of a complete device with a major obstacle being the ability to electrically gate devices. Here we demonstrate a fully functional multiterminal quantum dot device with integrated donor based in-plane gates epitaxially assembled on a single atomic plane of a silicon (001) surface. We show that such in-plane regions of highly doped silicon can be used to gate nanostructures resulting in highly stable Coulomb blockade (CB) oscillations in a donor-based quantum dot. In particular, we compare the use of these all epitaxial in-plane gates with conventional surface gates and find superior stability of the former. These results show that in the absence of the randomizing influences of interface and surface defects the electronic stability of dots in silicon can be comparable or better than that of quantum dots defined in other material systems. We anticipate our experiments will open the door for controlled scaling of silicon devices toward the single donor limit.
Due to the unprecedented rate at which our climate is changing, the ultimate consequence for many species is likely to be either extinction or migration to an alternate habitat. Certain species ...might, however, evolve at a rate that could make them resilient to the effects of a rapidly changing environment. This scenario is most likely to apply to species that have large population sizes and rapid generation times, such that the genetic variation required for adaptive evolution can be readily supplied. Emiliania huxleyi (Lohm.) Hay and Mohler (Prymnesiophyceae) is likely to be such a species, as it is the most conspicuous extant calcareous phytoplankton species in our oceans with growth rates of 1 day−1. Here we report on a validated set of microsatellites, in conjunction with the coccolithophore morphology motif genetic marker, to genotype 93 clonal isolates collected from across the world. Of these, 52 came from a single bloom event in the North Sea collected on the D366 United Kingdom Ocean Acidification cruise in June–July 2011. There were 26 multilocus genotypes (MLGs) encountered only once in the North Sea bloom and 8 MLGs encountered twice or up to six times. Each of these repeated MLGs exhibited Psex values of less than 0.05, indicating each repeated MLG was the product of asexual reproduction and not separate meiotic events. In addition, we show that the two most polymorphic microsatellite loci, EHMS37 and P01E05, are reporting on regions likely undergoing rapid genetic drift during asexual reproduction. Despite the small sample size, there were many more repeated genotypes than previously reported for other bloom-forming phytoplankton species, including a previously genotyped E. huxleyi bloom event. This study challenges the current assumption that sexual reproduction predominates during bloom events. Whilst genetic diversity is high amongst extant populations of E. huxleyi, the root cause for this diversity and ultimate fate of these populations still requires further examination. Nonetheless, we show that certain CMM genotypes are found everywhere, while others appear to have a regional bias.
In diverse animal species, from insects to mammals, females display a more efficient immune defence than males. Bateman's principle posits that males maximize their fitness by increasing mating ...frequency whereas females gain fitness benefits by maximizing their lifespan. As a longer lifespan requires a more efficient immune system, these implications of Bateman's principle may explain widespread immune dimorphism among animals. Because in most extant animals, the provisioning of eggs and a higher parental investment are attributes of the female sex, sex-role reversed species provide a unique opportunity to assess whether or not immune dimorphism depends on life history and not on sex per se. In the broad-nosed pipefish Syngnathus typhle, males brood and nourish the eggs in a ventral pouch and thus invest more into reproduction than females. We found males to have a more active immune response both in field data from four populations and also in an experiment under controlled laboratory conditions. This applied to different measures of immunocompetence using innate as well as adaptive immune system traits. We further determined the specificity of immune response initiation after a fully factorial primary and secondary exposure to a common marine pathogen Vibrio spp. Males not only had a more active but also a more specific immune defence than females. Our results thus indeed suggest that the sex that invests more into the offspring has the stronger immune defence.
Elevated environmental carbon dioxide (pCO2) levels have been found to cause organ damage in the early life stages of different commercial fish species, including Atlantic cod (Gadus morhua). To ...illuminate the underlying mechanisms causing pathologies in the intestines, the kidney, the pancreas and the liver in response to elevated pCO2, we examined related gene expression patterns in Atlantic cod reared for two months under three different pCO2 regimes: 380 μatm (control), 1800 μatm (medium) and 4200 μatm (high). We extracted RNA from whole fish sampled during the larval (32 dph) and early juvenile stage (46 dph) for relative expression analysis of 18 different genes related to essential metabolic pathways. At 32 dph, larvae subjected to the medium treatment displayed an up-regulation of genes mainly associated with fatty acid and glycogen synthesis (GYS2, 6PGL, ACoA, CPTA1, FAS and PPAR1b). Larvae exposed to the high pCO2 treatment upregulated fewer but similar genes (6PGL, ACoA and PPAR1b,). These data suggest stress-induced alterations in the lipid and fatty acid metabolism and a disrupted lipid homeostasis in larvae, providing a mechanistic link to the findings of lipid droplet overload in the liver and organ pathologies. At 46 dph, no significant differences in gene expression were detected, confirming a higher resilience of juveniles in comparison to larvae when exposed to elevated pCO2 up to 4200 μatm.
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•Larvae upregulate genes associated with fatty acid and glycogen synthesis under moderate ocean acidification (OA)•Larvae under high levels of OA fail to regulate•Dysfunctional metabolism and stress associated with pathologies in internal organs•Lack of differential gene regulation and stress response in juveniles correspond to a higher resilience to OA stress
Ocean acidification (OA), a direct consequence of increasing atmospheric CO
concentration dissolving in ocean waters, is impacting many fish species. Little is known about the molecular mechanisms ...underlying the observed physiological impacts in fish. We used RNAseq to characterize the transcriptome of 3 different larval stages of Atlantic cod (Gadus morhua) exposed to simulated OA at levels (1179 µatm CO
) representing end-of-century predictions compared to controls (503 µatm CO
), which were shown to induce tissue damage and elevated mortality in G. morhua. Only few genes were differentially expressed in 6 and 13 days-post-hatching (dph) (3 and 16 genes, respectively), during a period when maximal mortality as a response to elevated pCO
occurred. At 36 dph, 1413 genes were differentially expressed, most likely caused by developmental asynchrony between the treatment groups, with individuals under OA growing faster. A target gene analysis revealed only few genes of the universal and well-defined cellular stress response to be differentially expressed. We thus suggest that predicted ocean acidification levels constitute a "stealth stress" for early Atlantic cod larvae, with a rapid breakdown of cellular homeostasis leading to organismal death that was missed even with an 8-fold replication implemented in this study.
Abstract
Ocean acidification (OA), the dissolution of excess anthropogenic carbon dioxide in ocean waters, is a potential stressor to many marine fish species. Whether species have the potential to ...acclimate and adapt to changes in the seawater carbonate chemistry is still largely unanswered. Simulation experiments across several generations are challenging for large commercially exploited species because of their long generation times. For Atlantic cod (
Gadus morhua
), we present first data on the effects of parental acclimation to elevated aquatic CO
2
on larval survival, a fundamental parameter determining population recruitment. The parental generation in this study was exposed to either ambient or elevated aquatic CO
2
levels simulating end-of-century OA levels (~1100 µatm CO
2
) for six weeks prior to spawning. Upon fully reciprocal exposure of the F1 generation, we quantified larval survival, combined with two larval feeding regimes in order to investigate the potential effect of energy limitation. We found a significant reduction in larval survival at elevated CO
2
that was partly compensated by parental acclimation to the same CO
2
exposure. Such compensation was only observed in the treatment with high food availability. This complex 3-way interaction indicates that surplus metabolic resources need to be available to allow a transgenerational alleviation response to ocean acidification.
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