Day: 01/01/2012

How bacteria break a magnet.

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A magnetosensing bacterium bends its internal magnet to weaken it before cell division.

Bacteria that contain an internal compass face an unusual challenge when they come to divide: snapping their internal magnets in two. A report1 in the December issue of Molecular Microbiology explains how one species generates the force to separate magnetic nanoparticles and apportions them equally between daughter cells.

Richard Blakemore first described magnetotactic bacteria — which can orient themselves in line with Earth’s magnetic field — in the 1970s2. The magnets probably help oxygen-averse marine bacteria to navigate waters and sediments where the levels of chemicals such as oxygen and sulphide change quickly with depth, says Dirk Schüler, a microbiologist at the Ludwig–Maximilians University in Munich, Germany, who led the study1.

Bacteria build their compasses from tiny organelles called magnetosomes, which contain crystals of magnetite (Fe3O4) and and/or greigete (Fe3S4) other magnetic minerals. No single magnetosome produces a magnetic field strong enough to align a bacterium to Earth’s magnetic field, so the organelles gather together in a chain to form a stronger magnet.

When cells divide, however, they must create enough force to sever their magnets. Bacteria normally divide by first growing lengthwise and then constricting their cell walls at the centre, as if tightening a belt, until the walls meet and two cells are formed. But, says Schüler, belt-tightening doesn’t generate nearly enough force to tear apart a magnetosome chain.

Magnetochoreography

Using both light and electron microscopy, Schüler’s team tracked the bacterium Magnetospirillum gryphiswaldense as it split into two. Initially, the process followed the normal choreography of bacterial division: the cell lengthened and then slowly constricted at its centre. Next, however, the two soon-to-be daughter cells bent at up to a roughly 50-degree angle to one another, then rapidly broke off into two cells. The moustache-like bend was created because the cells were pinched into two on only one side, Schüler says.

Schüler’s team calculates that bending the magnetosome chain in this way would weaken the magnetic forces holding it together to the point at which it could be snapped in two. “If you break them like a stick, you’re talking about 10 piconewtons,” Schüler says — equivalent to the force normally produced during cell division.

The group’s experiments also explain how M. gryphiswaldense divides up its magnetosomes equally between the two cells. Schüler predicted that this would occur by chance alone, because each bacterium contains several dozen magnetosomes. But the researchers discovered that cytoskeletal proteins yank the magnetosome chain towards the centre when cell division begins, ensuring that the magnets are shared equally.

“The work is, in my opinion, top-notch,” says Dennis Bazylinski, a microbiologist at the University of Nevada, Las Vegas. He agrees that asymmetric cell division explains how M. gryphiswaldense snaps its magnet in two. However, other magnetotactic bacteria, a diverse group with many different shapes, may have come up with different solutions.

Bazylinski’s team is studying an organism tentatively named Magnetovibrio blakemorii (after Richard Blakemore) that keeps its magnetosomes spaced far apart, an arrangement that could make the chain easier to split.

Meanwhile, some magnetotactic bacteria produce multiple intertwined chains of magnetosomes, others dot the organelles within the cell membrane, and one strain maintains two chains, one at each end of the cell, says Arash Komeili, a microbiologist at the University of California, Berkeley. “My gut feeling is that some aspects of this process are unique to M. gryphiswaldense and not generalizable to all magnetotactic bacteria,” he says of Schüler’s work.

source:Nature

Fukushima reaches cold shutdown.

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But milestone is more symbolic than real.

The Japanese government announced that three reactors that suffered meltdowns in early March had officially reached “cold shutdown”. Perhaps inevitably, many in the press are reporting the announcement as a “major milestone” in the Fukushima saga. But in truth, cold shutdown will mean very little in any practical sense for what goes on at the plant. Nor is it likely to change the fate of the thousands of evacuees who were forced to leave their homes after the Fukushima crisis.

First a little bit about what the term technically means. Nuclear power reactors use energy from splitting atoms to heat water until it boils into steam. That steam is in turn used to turn a turbine, which produces power. When the nuclear reactions are halted, the reactor core doesn’t cool off right away. Instead, it continues to heat water to above boiling point. For a set period of time, usually a matter of hours after reactor is halted, it must be cooled actively with recirculated water. When the reactor temperature drops below 100 °C, active cooling is no longer needed in the reactor becomes passively safe. This is known in the business as cold shutdown.

All of the reactors that melted down at the Fukushima nuclear plant are now officially in “cold shutdown”.

As of 15 December, temperatures in the three reactor vessels known to have melted down were well below 100°C. According to the latest data from the Japan Atomic Industrial Forum, which tracks the reactors’ vital statistics, unit 1 is now at 38.3°C, unit 2 is at 68.7°C and unit 3 is at 64.1°C. The Tokyo Electric Power Company (TEPCO), which runs Fukushima, had imposed an additional requirement that the release of radioactivity is “under control and public radiation exposure by additional release is being significantly held down”. It has been months since any major release from the reactors, and it seems reasonable to consider this condition achieved as well.

But this is a cold shutdown like no other. Under normal conditions, operators could, theoretically at least, walk away from a reactor once cold shutdown is achieved. No more water needs be circulated, and as long as no one tries to restart the reactor core, it would sit there indefinitely. This is certainly not the case at Fukushima. For one thing, the reactors are leaking, and TEPCO must continue to inject water at the rate of around half-a-million litres a day, according to its latest press release. Moreover, the plant continues to pose an environmental risk, as evidenced by a recent leak from a system designed to decontaminate water flowing out from the core.

The truth is, this announcement is far more symbolic than it is practical. For another few years at least, it seems likely that the reactors will have to be actively pumped with water while their radioactive fuel slowly decays away. Meanwhile, residents who once lived near the plant will have to wait while the land around it is decontaminated — a process that involves the laborious removal of millions of cubic meters of topsoil.

Eventually, workers at the plant (or, far more probable, robots operated by workers) will open the reactor cores and remove the melted and charred remains of the fuel they once held. That fuel, together with contaminated soil, equipment, clothing and debris, will have to be disposed of at a yet-to-be-determined site somewhere in Japan. It’s an operation that will take many years, and more likely, many decades.

Meanwhile, the Japanese public and many of its politicians remained deeply mistrustful of the situation at Fukushima. In this week’s issue of Nature, two members of the Japanese parliament call for nationalization of the Fukushima Plant, to allow scientists and engineers to investigate exactly what happened inside the reactors, and to reassure the public that the decommissioning will be done with their interests at heart. Regardless of whether you agree with the authors, nationalization seems almost inevitable. The lengthy decommissioning process that will follow this cold shutdown, and the enormous cost involved, make it a job for a government, not a corporation.

Source:Nature

 

Particle physics is at a turning point.

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The discovery of the Higgs boson will complete the standard model — but it could also point the way to a deeper understanding.

Let’s tentatively agree that the Large Hadron Collider (LHC) detectors ATLAS and the Compact Muon Solenoid have discovered a Higgs boson, with a mass of about 125 gigaelectronvolts (GeV). Although standard statistical measures might not consider the situation settled, it seems very likely that there has indeed been a discovery at CERN, Europe’s high-energy physics lab near Geneva, Switzerland, given that two quite different detectors both see a signal of some significance at about the same mass, and that both see the expected signals in two or more channels.

This is a profound turning point in the quest for a fundamental unified theory of the physical world. The properties and mass of the LHC’s Higgs boson suggest that physicists will soon find superpartners for particles, and that we have begun to connect string theory to the real world.

The Higgs boson, an as-yet-unknown kind of matter thought to generate mass in other particles, is the final ingredient needed to complete and confirm the standard model of particle physics. This amazing theory describes the particles (quarks and leptons) and the strong, weak and electromagnetic forces that interact to make our world (with the addition of the theory of gravity). Quarks combine to make protons and neutrons; protons and neutrons to make nuclei; nuclei and electrons (a type of lepton) to make atoms, then molecules and chocolate and people and planets and stars and so on. The standard model has no puzzles or problems, and incorporates at a fundamental level everything from condensed-matter physics to astrophysics. It achieves the goals of four centuries of physics. The Higgs itself has been sought for decades: the main route through which its signal was reported at the LHC was the particle’s decay into two photons. Collaborators and I first studied this signal in the mid 1980s, as a possible method for detecting the Higgs boson at the Superconducting Super Collider, which was to be built at Waxahachie in Texas but was cancelled in 1993.

Besides completing the standard model, the discovery of the Higgs tells us that a future, deeper underlying theory of the law(s) of nature must include and account for fundamental Higgs bosons. (Physicists have suggested alternative theories that include oddities such as composite Higgs bosons, but the CERN discovery essentially excludes them.) That will extend the standard model, and go beyond it to illumi­nate issues such as supersymmetry and the origin of dark matter.

“The properties and mass of the Higgs boson  strongly suggest that we have begun to connect string theory to the real world.”

A major and unexpected clue to the future offered by the CERN discovery is that the reported Higgs boson signal seems to behave as if it were a ‘standard-model Higgs boson’. Under the standard model, this should not be possible, because relativistic quantum field theory shows that the Higgs’ mass must experience quantum corrections that are much, much larger than the mass itself. Because the masses of quarks, leptons and the W and Z bosons that mediate the weak force are themselves dependent on the Higgs mass, the standard model predicts masses for them many orders of magnitude larger than what we observe.

This can be fixed. When the standard model is extended to a supersymmetric theory, the nature of the predicted Higgs boson changes. Its mathematical behaviour improves and the resulting theory is realistic.

Physicists thought that a Higgs boson, when discovered, would take this supersymmetric form, so how have we discovered one so apparently identical to the impossible standard-model version? Working out how to interpret this could be a large step towards the underlying broader theory that will extend the standard model.

One explanation could come from an unexpected source: string theory or its extension, M-theory. Contrary to what you may have heard, predictions about the real world can be made from string theory, although the 10- or 11-dimensional theory must first be ‘compactified’ to 4 dimensions (with 6 or 7 small dimensions left curled up). There has been considerable progress on that, as well as on how to stabilize the fields that describe the curled-up dimensions.

My collaborators and I have shown that in generic string and M-theories — consistent with constraints from cosmology and incorporating the Higgs mechanism for generating mass — the lightest Higgs boson behaves very much like the standard-model Higgs boson. And it has a mass of about 125 GeV, just as observed.

We first reported these results at the inter­national String Phenomenology Conference in Madison, Wisconsin, in August; and just days before the CERN data were reported, we posted a paper containing a significantly more precise prediction .

The same string theory (actually M-theory) that predicts the Higgs mass correctly also predicts that a spectrum of superpartners and some of their associated signals should now be discovered at the LHC. Particles such as gluinos — superpartners to gluons, which mediate the strong force — have not yet been searched for explicitly in the decay modes predicted by the string theories, mainly decay to top and bottom quarks. They could be found in these modes by the middle of next year. If so, the discovery may have a lower profile than the news of the Higgs boson, but the implications could be even greater. String theory could have come of age at last.

Source:Nature

 

FDA Approves Anturol.

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The U.S. Food and Drug Administration (FDA) has approved Anturol (oxybutynin) topical gel 3% for the treatment of overactive bladder (OAB) with symptoms of urge urinary incontinence, urgency, and frequency.

Anturol is a topical, translucent hydroalcoholic gel containing oxybutynin, an antispasmodic, antimuscarinic agent. Applied once daily to the thigh, abdomen, upper arm or shoulder, an 84 mg (approx. 3 mL) dose delivers a consistent dose of oxybutynin through the skin over a 24-hour period, providing significant efficacy without sacrificing tolerability.

The approval of Aturol is based on a 12-week, multi-center placebo controlled Phase 3 clinical study conducted by Antares. Patients were randomized to either an 84 mg or 56 mg dose application of oxybutynin gel 3% versus placebo. The FDA approved the 84 mg dose application. Patients treated with 84 mg oxybutynin gel daily achieved steady state drug concentrations within three days and experienced a statistically significant decrease in OAB symptoms versus placebo, including the number of urinary incontinence episodes per week. Statistically significant improvements in daily urinary frequency and urinary void volume were also seen with the 84 mg dose.

The product was well tolerated in the study. The most frequently reported treatment-related adverse events (>3%) were dry mouth (12.1% versus 5% in placebo), application site erythema (3.7% versus 1.0% in placebo) and application site rash (3.3% versus 0.5% in placebo). Because the active ingredient is delivered transdermally, it is not metabolized by the liver in the same way as orally administered oxybutynin. This results in a low level of side effects, such as dry mouth and constipation.

Additional pharmacokinetic studies showed that showering one hour or later, or the application of sunscreen 30 minutes before or after gel application had no affect on the overall systemic exposure of the drug.

Patient Information for Anturol

Important: For use on the skin only (topical). Do not get Anturol in or near your eyes, nose, or mouth. Read this Patient Information carefully before you start taking Anturol and each time you get a refill. There may be new information. This information does not take the place of talking with your doctor about your medical condition or your treatment.

What is Anturol?

Anturol is a prescription medicine used to treat the symptoms of overactive bladder including:

  • a strong need to urinate with leaking or wetting accidents (urge urinary incontinence)
  • a strong need to urinate right away (urgency)
  • urinating often (frequency)

It is not known if Anturol is safe or effective in children.

source:FDA

Edarbyclor

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FDA Approves Edarbyclor

The U.S. Food and Drug Administration (FDA) approved Edarbyclor (azilsartan medoxomil and chlorthalidone) for the treatment of hypertension to lower blood pressure in adults. Edarbyclor is the only fixed-dose therapy in the U.S. to combine an angiotensin II receptor blocker (ARB) with the diuretic chlorthalidone in a once-daily, single tablet. The recommended starting dose of Edarbyclor is 40/12.5 mg and the maximum dose is 40/25 mg.

The two medications in Edarbyclor work to help lower blood pressure in patients with hypertension. Azilsartan medoxomil, marketed as Edarbi in the U.S., reduces blood pressure by blocking the action of angiotensin II, a vasopressor hormone that naturally exists within the body. When Edarbi blocks the angiotensin II receptor, blood vessels can stay relaxed and open, and blood pressure can be reduced. Chlorthalidone reduces the amount of water in the body by increasing the flow of urine, which helps to lower blood pressure. Prior landmark clinical outcomes trials have demonstrated that chlorthalidone is effective in reducing blood pressure in patients with hypertension and that long-term use is associated with reductions in serious hypertension-related complications.

source:FDA

Poor maternal–child relationships associated with increased risk for adolescent obesity.

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The quality of early emotional maternal–child relationships was shown to affect the risk for adolescent obesity in a prospective analysis recently published in Pediatrics.

“Obesity is affecting even preschool-aged children, and we lack effective approaches for prevention,” the researchers wrote. “We provide evidence that the quality of the early maternal–child relationship is associated with risk for adolescent obesity.”

More than one-quarter of toddlers with the lowest-quality emotional relationship with their mothers were obese as teens, according to the researchers.

Using data from the Study of Early Child Care and Youth Development, researchers assessed child attachment security and maternal sensitivity for 977 participants at 15, 24 and 36 months of age. The number of times a child was insecurely attached or experienced low maternal sensitivity at any of the three ages dictated a maternal–child relationship quality score; a score of at least 3 was considered a poor-quality relationship.

A BMI of at least the 95th percentile at age 15 years was considered obese.

Nearly 25% of participants had poor-quality maternal–child relationships (24.7%) vs. 22% of participants who were neither insecurely attached nor experienced low maternal sensitivity at any age.

The rate of adolescent obesity was 26.1% for those with a score of at least 3; 15.5% for those with a score of 2 and 13% for those with a score of 0.

The odds of adolescent obesity were 2.45 times higher in participants with the poorest quality maternal–child relationships compared with those with the highest quality relationships (95% CI, 1.49-4.04). Compared with insecure attachment, low maternal sensitivity was more strongly associated with adolescent obesity, the researchers wrote.

Source:Endocrine Today

 

American Thyroid Association: Better communication among care team critical for optimal care, surveillance

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Physicians who treat patients with thyroid cancer as part of a multidisciplinary treatment team need specific perioperative information, including results from clinical examination, biochemical testing, and cross-sectional and functional imaging tests, among other sources.

Communication between disciplines is critical, but the American Thyroid Association recognized that there was no universally accepted model for effectively sharing this data among the various care providers. The association’s Surgical Affairs Committee was tasked with identifying critical information that should be readily available to each member of the multidisciplinary team. The goal was to help physicians develop a management plan for each patient that will lead to a rational, risk-based approach to initial therapy, adjuvant therapy and follow-up studies.

The committee identified three distinct types of data that must be shared: preoperative evaluations, intraoperative findings and postoperative data, events and plans. The committee provided several data points in each category such as comorbid conditions and abnormal laboratory values that could influence decisions about adjuvant radioiodine ablation therapy in the preoperative category, extent of surgery and description of gross extrathyroidal extension from the intraoperative findings and vocal cord dysfunction and anticipated after-care plan from the postoperative findings.

“Accurate communication of the important findings of thyroidectomy is critical to individualized risk stratification, as well as to the short-term follow-up issues of thyroid cancer care that are often jointly managed in the postoperative setting,” committee member R. Michael Tuttle, MD, of the Memorial Sloan-Kettering Cancer Center, and colleagues wrote. “Moreover, true multidisciplinary communication is essential to providing optimal adjuvant care and surveillance

Source:Endocrine Today.

 

 

 

 

Newfound Gas Cloud Points to Possible Planets Near the Milky Way’s Black Hole

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Times are tough on planet Earth right now, but at least we don’t have a supermassive black hole lurking just over the horizon.

A new study suggests that stars near the Milky Way’s central black hole may well form planets. The researchers based their analysis on a very recent discovery of a gas cloud making its way toward the galactic center.

On December 14 an international team of astronomers led by Stefan Gillessen of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, announced that they had spotted something heading toward a close encounter with the central black hole, known as Sagittarius A* (Sgr A*), which has as much mass as four million suns. Gillessen and his colleagues interpreted the object to be a dusty gas cloud about three times as massive as Earth, possibly belched out as stellar winds (plasma streaming outward from stars) from the young stars that orbit the black hole.

A few days later, Ruth Murray-Clay and Abraham Loeb of the Harvard–Smithsonian Center for Astrophysics suggested that the newfound object may be much more closely connected to those stars. In a preprint posted to the Web site arXiv.org on December 20, Murray-Clay and Loeb say that the cloud Gillessen and his colleagues discovered could be the disrupted remnants of a planet-forming disk surrounding a star that used to orbit Sagittarius A* at a safe distance but is now plunging toward the black hole. A protoplanetary disk is the swirling pancake of gas and dust surrounding a young star, which can coalesce into planets, asteroids and comets. “This cloud of gas naturally originates from a proto-planetary disk surrounding a low-mass star, which was scattered a century ago from the observed ring of young stars orbiting Sgr A*,” they write.

The star itself would be too faint to see. But as Sagittarius A* has distorted and fried the disk with the black hole’s gravitational pull and the radiation of its environs, it has generated a debris stream around the star that telescopes can detect.

If the young stars orbiting Sagittarius A* host protoplanetary disks, that “implies that planets form in the Galactic centre,” the researchers write. But you wouldn’t want to live on one of those worlds. The galactic center is awash in intense radiation emitted by material swirling around the outside of the black hole, which gets compressed and heated as it falls inward. (It is that radiation from outside the event horizon that allows astronomers to “see” a black hole, which itself holds tight to all matter and photons and hence emits no light.)

Plus there’s always the chance that your host star will get knocked onto an orbit heading right for the black hole, as Murray-Clay and Loeb suspect has happened here. In some cases, the researchers suggest, planets might be torn apart by the black hole’s gravitational pull and produce bright flares as the pieces fall in.

We should soon find out whose explanation for the gas cloud is correct. The cloud, whatever its origin, is on track to swing past Sagittarius A* in mid-2013. If it’s a simple gas cloud, it will get torn apart and partly consumed by the black hole, temporarily brightening the radiation from around Sagittarius A*. If the cloud instead comprises debris from a protoplanetary disk, the star itself should cruise past Sagittarius A* largely unscathed. But the cloud will grow denser as more and more mass from the disk is dragged away from the star. Either way, it ought to be quite a show.

 

source:Scientific American.

 

Solar Wind May Explain Planet Mercury’s Puny Magnetic Field.

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Computer models suggest a so-called dynamo process in the planet’s molten core is dampened by the solar wind.

The mystery of why Mercury‘s magnetic field is so weak may just have been solved: It is being stifled by the solar wind, researchers think.

Mercury and Earth are the only rocky planets in the solar system to possess global magnetic fields, and for years scientists have puzzled over why Mercury’s is so flimsy. Roiling molten iron cores generate magnetic fields, and given how extraordinarily iron-rich Mercury is for its size — its metallic heart may comprise two-thirds of Mercury’s mass, twice the ratio for Earth, Venus or Mars — the innermost planet should have a magnetic field 30 times stronger than what spacecraft such as NASA’s MESSENGER probe have detected so far.

To study Mercury’s magnetic field, researchers created 3-D computer simulations of the planet’s interior and of the solar wind, the deluge of energetic particles from the sun that constantly bombards its nearest planet.

The computer models suggested that the churning of Mercury’s molten iron core ordinarily would amplify the magnetic field up to Earth-like levels, in a so-called dynamo process like the one within our planet. [The Greatest Mysteries of Mercury]

However, the onrushing solar wind likely prevents that from happening, researchers said.

The study found that the solar wind deflects charged particles in the shell around the planet known as a magnetosphere. The magnetic field of this magnetosphere reaches all the way to Mercury’s core, limiting the strength of the field created by the planet’s interior, researchers said.

“The magnetic coupling between the magnetosphere and the dynamo in the planetary interior yields a weakened dynamo that can explain the enigmatic weakness of the magnetic field of Mercury,” said study lead author Daniel Heyner, a physicist at Technical University in Braunschweig, Germany.

Scientists plan to test the accuracy of their models using data on Mercury’s magnetic field and magnetosphere collected by MESSENGER and by the European BepiColombo mission due to launch in 2014, researchers said.

“This is quite a challenge, as the magnetosphere is small and very dynamic,” Heyner told SPACE.com.

The growing number of alien planets that astronomers are discovering around distant stars may also offer insights into how planetary dynamos “are controlled by the stellar wind of stars that are in a different evolutionary phase compared to our sun,” Heyner added.

Source:Scientific American.

 

 

 

 

 

 

Percutaneous Nephrolithotomy safe in chronic kidney disease

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Chronic kidney disease does not rule out percutaneous nephrolithotomy (PCNL), say researchers from Turkey.

“PCNL does not affect kidney function even in patients with limited kidney function,” lead investigator Dr. Tolga Akman told Reuters Health by email. “Single tract as well as multitract PCNL can be safety performed in patients with chronic kidney disease (CKD).”

As reported online November 17 in The Journal of Urology, Dr. Akman and colleagues at Haseki Teaching and Research Hospital in Istanbul reviewed the long-term outcomes of 177 CKD patients who underwent PCNL – including 142 who had one-access PCNL and 35 who had multitract procedures.

Twenty-seven patients (15.3%) had one or more complications, including blood transfusions in 17 patients (9.6%), one case of pelvicalyceal system perforation, five cases of urosepsis, six instances of transient fever, and three cases of acute renal failure.

The average follow-up interval was 43 months. Renal function stage was improved from baseline in 52 patients (29.4%), maintained in 96 patients (54.2%), and worse in 29 patients (16.4%).

Diabetes and the occurrence of complications were the only independent factors associated with kidney function deterioration. Hypertension did not appear to affect kidney function in this cohort.

Eighty percent of patients were stone-free at three months, but a quarter of this group had stone recurrence during long-term follow-up.

“Comprehensive metabolic evaluation, stone composition analysis, and metaphylaxis may aid in minimizing stone recurrence and the growth of residual stones after PCNL,” the researchers suggest.

“It is important to make efforts to minimize complications in this population, including the consideration of referral to surgeons with ample experience with PCNL,” they add.

Dr. Akman suggests that PCNL could become a standard treatment for patients with CKD who have renal stones that are larger than 2 cm and resistant to shock wave lithotripsy.

“PCNL, RIRS (retrograde intrarenal surgery) and SWL (shock wave lithotripsy) are treatment alternatives for kidney stone in patients with CKD,” Dr. Akman added.

Source: Journal of Urology.