Explore further © 2010 PhysOrg.com More information: Bruce Kane. “Levitated spinning graphene flakes in an electric quadrupole ion trap.” Phys. Rev. B 82, 115441 (2010). DOI:10.1103/PhysRevB.82.115441 . “Levitated Spinning Graphene.” arXiv:1006.3774v1 via: Popular Science (PhysOrg.com) — At 60 million rotations per minute, a two-dimensional sheet of graphene has become the fastest-spinning trapped macroscopic object ever. Graphene is known for its large strength, and it’s this strength that enables the material to not be pulled apart into pieces when spun at such a high rate. Made of a single sheet of carbon atoms, graphene can be spun at the fastest rate of any known macroscopic object. Image credit: Wikimedia Commons. Light-speed nanotech: Controlling the nature of graphene Citation: Rapidly rotating graphene is fastest-spinning macroscopic object ever (2010, September 30) retrieved 18 August 2019 from https://phys.org/news/2010-09-rapidly-rotating-graphene-fastest-spinning-macroscopic.html Physicist Bruce Kane of the University of Maryland in College Park has published his study on the spinning graphene in a recent issue of Physical Review B. His main ambition was to measure and modify graphene by suspending micrometer-sized flakes of the material in an ion trap. As electric fields trapped and suspended the charged graphene flakes, Kane set up a circularly polarized light beam to transfer a large amount of angular momentum to the flakes, causing them to spin at a very high rotation frequency. “This high rotation frequency, facilitated by the ability of graphene to withstand centrifugal tension during rotation, is, to the author’s knowledge, the largest ever measured for a macroscopic trapped object,” Kane wrote in a paper posted at arXiv.org.Kane also explained that the graphene flakes are spinning at only one-thousandth of their theoretical maximum rate, which is calculated based on graphene’s estimated strength. Modifying the experimental set-up could enable the graphene to be spun even faster. As Kane explained in his study, graphene, which was discovered in 2004, is the first truly two-dimensional system, meaning that its electronic, mechanical, and thermodynamic properties are all determined by the structure of a single sheet of carbon atoms. Since placing graphene on a substrate can interfere with measuring its properties, this new method of levitating and spinning graphene could allow researchers to investigate, grow, and manipulate sheets of graphene with greater ease. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
Citation: Origin of the Eukaryotic cell: Part I – How to train your endosymbiont (2014, December 4) retrieved 18 August 2019 from https://phys.org/news/2014-12-eukaryotic-cell-endosymbiont.html How did complex life evolve? The answer could be inside out Credit: Cold Spring Harbor Press Among the questions most poignately raised by the hydrogen hypothesis are what was the actual genetic contribution to the eukaryote, and when exactly did this purported mass mitochondrial gene exodus take flight across the Red Sea cytoplasm to nucleus. Some clues come from the chapter by David Moreira and Philippe Deschamps, which like others, looks more broadly at the question of endosymbiont acquisition. In particular, they do a phylogenetic analysis of plastids, the photosynthetic apparatus possed by some eukaryotes. It is now widely believed that photosynthesis began in eukaryotes by endosymbiosis with cyanobacteria. This event would have resembled the previous mitochondrial mergers only it is now estimated to have ocurred roughly 500 million years later.The book is not without occaisional claims of “settled science,” as a subsequent chapter by Michael Gray indicates. This is probably forgiveable because he gets around to making some good points. Within his unseen circle of confidence he offers that while the DNA of mitochondria (mtDNA) is “unquestionably the remnant of a-proteobacterial genome,” he reveals that only 10%-20% of the mitochondrial proteome is demonstrably alphaprotobacterial in origin. Gray’s “pre-endosymbiont hypothesis” suggests that the host cell that accomodated the new symbiont may have already had genes for several of the many non-energy generating functions found in a contemporary mitochondrion already esconced away in a membrane-bound metabolic organelle which he calls a premitochondrion. Just to clarify, this couterflow of gene products from an extant endogenous compartment to the new symbiont would exist in tandem with a background flux of new symbiont genes encoding proteins for the symbiont (which must then somehow acquire organelle localization signals) to the nucleus.We might call this hypothetical endogenous premitochondrial organelle a “dark endosymbiont” in the spirit of the dark matter that is inferred to exist, or must have existed at some point in the past in our universe. In their chapter on plastids, Moreira and Deschamps note that genetic analysis has previously led others to propose similar kinds of cryptic organelles that are no longer visible in the cell. While these kinds of things are certainly possible, Cavalier-Smith is quick to point out the limitations of what he refers to as molecular myopia and mythical molecular clocks. Without some other kind of analysis to back it up, even if it is just protein conformation comparisons for example, molecular sequence alone invariably leads to ambiguous or even contradictory conclusions. As the gaps in knowledge of the origins of the eukaryotic cell are now being rapidly filled in, it seems that it is becoming more difficult to accept any one part of any broad proposal for a definitive tree of life without accepting the whole thing. One good example of how to quickly get confused when favoring a gene-centric approach at the expense of paleontologic or structural organelle-level analysis is with ribosomes. While horizontal, lateral and verticle gene flow among bacteria, archaea, and eukaryotes are constant confusers across species, the ribosomal RNA and riboproteins that exist in several unique cell-trafficking or inheritance scenarious in the organelles of single cell can be even more confounding. Cavalier-Smith has offered several ideas here to explain the size changes that have occured in the evolution of particular ribosomal subunits found in mitochondrial and nuclear DNA, as well as the localization motifs they have. In a follow up post we will address some of the main structural features of cells that have been critical in defining the evolutionary path taken by eukaryotes. Chief among these are the different ways that various kingdoms of life make their membranes, cytoskeletons, and cilia. We will also explore the precursors to spliced introns, centrioles, meisosis, recombination, sex, and perhaps multicelluarity. The finer scale structure of golgi, and the bacterial precident for mitochondrial cristae should also be included. Finally we will look at some attempts to root major eukaryotic developments in terms of the ecological background of Earth, its oxygenation, and maybe even a glaciation event or two. © 2014 Phys.org This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. More information: The Origin and Evolution of Eukaryotes: cshperspectives.cshlp.org/cgi/ … lution_of_eukaryotesPart 2 of the story is here: phys.org/news338016128.html The nearest the book comes to providing that holy explanation is undoubtedly the chapter by Thomas Cavalier-Smith dealing with what he likes to call the “Neomuran Revolution,” which we will describe below. At its heart, what Cavalier-Smith offers is a sweeping tree of life that has continued to grow with the abundant fertilizer he has added over the last several decades. Incidentaly, we should add that one of the best ways to expedite your ascendance to prominance in the origin of life business is to simply expand your last name with – Smith. Both Graham Cairns-Smith and John Maynard Smith were masters at this and their work continues to shape the field.Instead of the typical three domains of life—bacteria, archaea (archaebacteria), and eukaryotes—that many now presume, Cavalier-Smith maintains that the latter two form a sister clade (neomura), whose origins refute the now popular theory that eukaryotes originated by merging an archaebacterium with an alphaproteobacterium. The defining feature of clade neomura, he suggests, is the loss of the murein wall in certain posibacteria—his world for a refined class of gram-positive bacteria. This evolution, taking place ~1.2 Gy ago, would have enabled a more flexible cell complete with novel modes of cell division, DNA segregation, phagocytosis, and ambulation.The departure of some of Cavalier-Smith ideas from the current mainstream view takes root with the so-called “hydrogen hypothesis” which we discussed here fairly recently. When extended to its logical conclusion, this theory presumes that the above-mentioned merger that enabled the aquisition of a mitochondrial precursor (the alphaproteobacterium) by a methanogen (the archaeobacterium) precipitated the development of a complex nucleus through subsequent gene transfer from the mitochondrion, along with the prompt establishment of the other modern accoutrements of the eukaryotic cell. Explore further (Phys.org)—”The origin and evolution of eukaryotes” is a tale that has yet to be told. At this point in time, it exists only as the title of a fascinating new compendium that has just been produced by the Cold Spring Harbor Press. While this volume is some 400 pages long, there is a palpable feeling among its authors that if they could somehow just compact it into a few pages, a figure, and perhaps even a token energy equation, then what is now just a diffuse description would become the explanation we seek—maybe even without any new discoveries or information.
More information: Jordan Venderley et al. Evidence of pair-density wave in spin-valley locked systems, Science Advances (2019). DOI: 10.1126/sciadv.aat4698 Sajedeh Manzeli et al. 2-D transition metal dichalcogenides, Nature Reviews Materials (2017). DOI: 10.1038/natrevmats.2017.33Román Orús. A practical introduction to tensor networks: Matrix product states and projected entangled pair states, Annals of Physics (2014). DOI: 10.1016/j.aop.2014.06.013 E.M. Stoudenmire et al. Studying Two-Dimensional Systems with the Density Matrix Renormalization Group, Annual Review of Condensed Matter Physics (2011). DOI: 10.1146/annurev-conmatphys-020911-125018 Evidence of PDW oscillations. (A) Arg (Δsinglet⟨ij⟩) for all nearest-neighbors with U = +2 for the 3 by 36 lattice simulated with periodic boundary conditions along the short direction and open boundary conditions along the long direction. For visibility, the scientists truncate the plot so that only the third farthest from the edge field is shown. The line thickness is proportional to the pairing amplitude. (B) The scientists plot the real and imaginary components of Δsingletij and Δtripletij for i,j along the middle rung of the lattice to present the phase oscillations. Credit: Science Advances, doi: 10.1126/sciadv.aat4698. To capture the spin-valley locked Fermi surfaces in one-band model in the valence group VI TMDs, the scientists considered a nearest-neighbor tight-binding model on the Fermi surface, where the magnetic flux introduced small amounts of anisotropy in the pockets, analogous to those observed in real semiconductor materials such as MoS2, followed by the inclusion of on-site interactions. In the present work, the DMRG simulation unexpectedly revealed a tendency to break translational symmetry in the repulsive interaction regime to form a modulated pair state, after which the scientists observed evidence of the formation and maintenance of robust PDW oscillations, despite changes (increase) in the simulated chemical potential. This observation by Venderley and Kim was the first report of a strong coupling-driven PDW within DMRG simulations of a simple fermionic model. The phase oscillations plotted in this study, strongly resembled the PDW-type behavior reported in the earlier 1D Kondo-Heisenberg model.Venderley and Kim then Fourier transformed these oscillations to suggest that the infinite momentum of the Cooper pairs originated from the interplay between the Fermi pockets. This view was reinforced when they probed the effect of increasing the chemical potential in the study (which decreased the pocket radius). They then captured oscillations in the singlet pairing strength and in the bond charge density to show that both orders were dominated by the same Fourier mode. Modelling the Fermi surface. (A) The spin-dependent staggered flux pattern for one-spin component with ± Φ flux per plaquette. An opposite flux pattern for the other spin component guarantees time-reversal symmetry. The arrows indicate the direction of positive phase hopping. (B) The Fermi surface in the tight-binding model as derived in the study. Here, the spin-valley locked, circular Fermi pockets are evident. Credit: Science Advances, doi: 10.1126/sciadv.aat4698. Recent discoveries in high Tc superconductors have resulted in an intense interest in a “pair-density wave” (PDW) formed in Cooper pairs (an electron pair bound together at low temperatures), although there is little theoretical understanding on the driving mechanisms of this exotic state. The complexity results from the many competing states that are in close energy in the strongly correlated region within seemingly simple models and phenomena such as the Hubbard model, frustrated magnets and high temperature superconductors. In a recent study, Jordan Venderley and Eun-Ah Kim at the Cornell University, New York, showed that inversion symmetry breaking and resulting spin-valley locking could promote PDWs to overcome the more commonly found spin and charge stripes through frustration against magnetic order. The study detailed the first robust evidence for a PDW in density matrix renormalization of a simple fermionic model via group simulation. The outcomes pointed to an intriguing possibility of the exotic state occurring in hole-doped group VI transition metal dichalcogenides (TMDs) with spin-valley locked band structure and moderate correlations. The results are now published in Science Advances. High temperature superconductors (abbreviated high-Tc) are materials that behave as superconductors at extremely high transition temperatures. The first experimental evidence of superconductors was discovered by J.G. Bednorz and K.A. Müller at IBM’s Zurich Research Lab in 1986, for which they were subsequently awarded the Nobel Prize in Physics in 1987. Recent experimental and theoretical developments revived the idea of a regulated or modulated superconducting state that spontaneously breaks translational symmetry. Early efforts on regulating superconductors have closely maintained the principles in the original Fulde-Ferrell-Larkin-Ovchinnkov (FFLO) model, proposed in 1964. An alternative proposal for a modulated paired state for cuprates (materials containing copper anionic complexes) requires a strong coupling mechanism, known as a pair-density wave (PDW), which is distinct from FFLO-type superconductors. Fourier decomposition of the PDW and bond charge order. (A) Fourier transforms of the PDW and charge bond order. Zero momentum, i.e., constant contributions and decay effects have been removed. (B) Depiction of pairing in momentum space. The regions demarcated by dashed lines are the approximate pairing regions. Credit: Science Advances, doi: 10.1126/sciadv.aat4698. While many models exist in different branches of physics, the Hubbard model is an iconic and simple contrivance of theoretical condensed matter physics that captures the behavior of correlated electrons in solids as they hop between lattice sites. In the present study, Venderley and Kim therefore turned to a Hubbard model and expected for the frustrating magnetic spin order to nudge systems into a PDW state on a frustrated triangular lattice with broken inversion symmetry. The model captured the hole-doped monolayer group IV TMDs, used as benchmark systems to study and control intertwined electronic orders, fueled by exotic possibilities driven by spin-orbit-coupling (SOC) and a lack of centrosymmetry, alongside superconductivity as observed in preceding studies. Explore further Atoms stand in for electrons in system for probing high-temperature superconductors Effect of chemical potential on the simulated PDW phase structure demonstrated in the study. The phase of the bond-centered singlet superconducting order parameter, for nearest-neighbors on the 3 × 36 lattice with random pair-edge-field where a larger chemical potential of µ = 6.0 is used rather than µ = 4.6. Here, the line thickness is proportional to the amplitude. The lattice has periodic boundary conditions along the short direction and open boundary conditions along the long direction. Increasing the chemical potential, μ, from μ = 4.6 to μ = 6.0 only enlarges the unit cell by an additional lattice site. Credit: Science Advances, doi: 10.1126/sciadv.aat4698. © 2019 Science X Network In this way, Venderley and Kim used DMRG to study superconducting tendencies of a repulsive U Hubbard model on a triangular lattice with spin-valley locking. They probed the tendencies to reveal the complex superconducting phase diagram of the model with translational symmetry-breaking superconducting states; possibly in competition with a uniform state. While researchers are interested in modulating superconducting states, the observed was the first report of a strong coupling-driven PDW formed in a simple fermionic model. Venderley and Kim next aim to investigate if the observed PDW state can be found in a truly 2-D setting by using a different numerical technique such as the density matrix embedding theory that has shown high quality results in 2-D Hubbard models. The isolation of graphene more than a decade ago transformed the landscape of condensed-matter physics, as the single-atom-thick, two-dimensional material exhibited high crystal and electronic quality to represent a conceptually new class of quantum materials. Physicists and engineers have since explored a vast family of two-dimensional crystals known as transition metal dichalcogenides (TMDs) in which electrons exist in layers with insulating, conducting or semiconducting properties, although little attention has been directed to investigate superconductivity in the 2-D crystals. Ongoing work in the field continues to provide surprisingly fertile ground for applications in low dimensional physics. Citation: Evidence of pair-density wave (PDW) in spin-valley locked systems (2019, April 9) retrieved 18 August 2019 from https://phys.org/news/2019-04-evidence-pair-density-pdw-spin-valley.html The DMRG (density matrix renormalization group) is a powerful nonperturbative method used to study strongly interacting electronic systems and explore a diverse selection of strongly correlated, competing quantum phenomena. The DMRG technique was established in the past decade as the leading method to simulate statics and dynamics of one-dimensional quantum lattice systems, with potential for further development. To access the system’s superconducting tendencies, Venderley and Kim implemented a pair-edge field motivated by the field-pinning approach, which underlay several previous studies. They biased the system to a specific superconducting state and studied the emergent symmetry of the appropriate order parameter in the bulk to deduce the model’s inclination towards various instabilities. The scientists conducted the DMRG calculations and DMRG simulations in two dimensional systems using the iTensor Library developed by Stoudenmire and White. They presented the DMRG simulations in a cylinder with three-unit cells in the periodic direction and 12-, 18-, 24- and 36-unit cells in the nonperiodic direction. The width of the simulation was sufficiently large to sample the pockets in the Fermi surface but not so large as to make the DMRG prohibitively expensive for the computational resources in the lab. Lattice and edge field. A depiction of the lattice in the study. It is periodic in the short direction with three-unit cells and has open boundaries in the long direction. The ellipses on the right signify that multiple lengths are studied: L = 12, 18, 24, 36. The edge field, shown as red lines, is a pair field of the form derived in the study. The nearest-neighbor hopping structure for spin up is also shown with the spin down hopping structure being the complex conjugate of that shown above. Credit: Science Advances, doi: 10.1126/sciadv.aat4698. Journal information: Science Advances The existing need for a strong coupling mechanism led physicists to search for the PDW state in numerical simulations. Present evidence of a PDW in the density matrix renormalization group (DMRG) was only established in the one-dimensional (1D) Kondo-Heisenberg model. Numerical evidence from the controlled approach of the DMRG is, however, lacking in simple fermionic models. A signature difficulty in realizing such a state is due to the presence of spin and charge stripe ground states instead of the PDW state on a Hubbard or t-J model in a square lattice with open-rotation symmetry. The t-J model, first derived from the Hubbard model by Josef Spalek in 1977, described strongly-correlated electron systems to calculate states of high temperature superconductivity in doped antiferromagnets (composed of a few Fe atoms on a surface exhibiting two magnetic states). This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
KOLKATA: The 43rd Annual Convocation of the Rabindra Bharati University (RBU) on Tuesday witnessed D. Litt degrees being conferred on eminent Indian classical vocalist Pandit Amiya Ranjan Bandyopadhyay, writer Nabaneeta Dev Sen and renowned painter Shri Jatin Das. Among others, the Hirachand Dugar Memorial Award 2018 was presented to Rabindranath Mondal. The West Bengal State Akademi of Dance Drama Music and Visual Arts Awards were presented to eminent danseuse Purnima Ghosh, theatre personality Pankaj Kumar Munshi, noted singer Ruma Guha Thakurta and renowned sculptor Prof Niranjan Pradhan. The Acharya Dinesh Chandra Sen Memorial Award for folklore research was conferred on Dr Sukhbilas Barma. Also Read – Heavy rain hits traffic, flightsHeld on the varsity’s Jorasanko Campus, the convocation was presided over by Bengal Governor Keshari Nath Tripathi, who also happens to be the Chancellor of the University. The Guest-in-Chief at the Convocation was Professor Furqan Qamar, Secretary General, Association of Indian Universities, who delivered the Convocation address. “Ninety-five scholars were awarded their PhD degrees and ninety-nine scholars received their MPhil degrees at the convocation. There were Also Read – Speeding Jaguar crashes into Merc, 2 B’deshi bystanders killedthirty-nine recipients of the Rabindra Bharati University Medal,” said Debdatta Roy, acting Registrar, RBU. Vice-Chancellor of the varsity, Sabyasachi Basu Ray Chaudhury read out his report, conferred degrees and diplomas on eligible candidates in absentia,and also awarded the medals and prizes.It may be mentioned that the varsity had plans to confer D. Litt on Amitabh Bachchan. The university had written him a letter expressing their desire to award him but the actor responded saying he would not be able to turn up because of his hectic shooting schedule.
The three children were later identified as siblings Rumana (7), Raja (5) and Sanya (4). They live with their parents in central Delhi’s Nabi Karim area, not very far away from the railway station, and were somehow stranded on Tuesday evening. It was the eldest sister, Rumana, who could recall the identity of a building (milestone) near her residence and they were finally handed over to their mother around 2.30 am, said Sanjay Bhatia, Deputy Commissioner of Police (Railways). He further said the children were located after 12 am, after which it took the police more than two hours to locate their residence. Also Read – Company director arrested for swindling Rs 345 croreIt was the Deputy Commissioner of Police (North), Madhur Verma, who came across the photograph on Twitter around 11 pm and communicated the matter immediately to the police post at New Delhi Railway Station. He also rushed to the spot with a police team.The concerned Twitter blogger also cooperated and said that it was at platform 16 (near Ajmeri Gate) where he had spotted the three children. But the kids were not present when a police team reached the said location. They then started searching all the platforms thoroughly and they were located finally at platform 1 (near Paharganj). It later emerged that the father of the three had left for Kanpur on Tuesday evening. When their mother, identified as Tabassum (37), could not find them for a very long time, she assumed that their father had taken them with him and did not report the matter to the police or even her neighbours. It is possible that the children followed their father, without him being aware of it, and later got stranded.
Kolkata: Soon, Housing Infrastructure Development Corporation (HIDCO) will construct a state-of-the-art library.A high-level meeting to discuss the matter was held on Thursday afternoon. Debashis Sen, chairman HIDCO, chaired the meeting. Senior officials of HIDCO were present along with Professor Dhubajyoti Chatterjee, Vice-Chancellor of Amity University, Professor Arun Kumar Chakraborty, director general national Library, Anuradha Biswas, stakeholder and Porinita Hati, architect and Neena Desai director C-DAC. Also Read – Heavy rain hits traffic, flightsThe proposed library will come up on the third and fourth floors of Nazrul Tirtha. It will be a state-of-the-art library with all modern facilities. Like all modern libraries, there will be cubicles for research scholars, which they can hire and carry on with their work. There will be some rooms. There will be both text and reference books of all the subjects. There will be a children’s section. Books will also be available online. Books on career counselling and foreign language will be kept at the library. Also Read – Speeding Jaguar crashes into Merc, 2 B’deshi bystanders killedA smart card will be given to the members. There will be a drop box where members can drop their books when the library remains closed or they are moving out of the city.Steps will be taken to stop damage of books and their theft. It is often found that important pages are torn or the members haven’t returned priceless books.New Town is coming up as a major health education hub in Bengal along with country’s biggest urban park and other state of the art facilities. It is a green city where creation of the state of the art library has always been felt. Even in Swapno Bhor, the only senior citizen’s park in the state, there is a library. At Nazrul Tirtha, an archive on Kazi Nazrul Islam has been set up. The residents as well as those who stay outside Rajarhat and research scholars can be a member of the library.
“In Aden, the raids began at around 10:00 pm (1900 GMT) on Thursday and were the most violent since the start of ‘Operation Decisive Storm’,” a resident of the southern city told AFP.The air strikes lasted well into the night, said other residents of Aden, especially the municipal headquarters of Dar Saad at the city’s northern entrance.They were carried out a few hours after Huthi Shiite rebels and renegade army soldiers loyal to former president Ali Abdullah Saleh arrived at the building, according to the residents. Also Read – Pro-Govt supporters rally as Hong Kong’s divisions deepenCoalition aircraft also targeted other positions, including a stadium in the centre of the city and checkpoints manned by the rebel forces. There was no way to immediately verify the reports.”Extremely violent” air raids also targeted Ataq, the capital of Shabwa province east of Aden which was seized by Saleh’s forces on Thursday, an official said. Strikes were launched against a missile base near the town and an arms depot at a base in Morra, to the west of Ataq, said another official.Rebel positions were been targeted around the city of Lahj, north of Aden, according to residents.The Saudi-led coalition launched the air strikes against the Huthi Shiite rebels on March 26 in support of President Abedrabbo Mansour Hadi after they seized the capital and forced him to flee to Aden and later Riyadh.