Tuesday, November 25, 2008

heat 99.hea.333330002 Louis J. Sheehan, Esquire

Attend enough talks about the future evolution of the universe, and you’re sure to hear a speaker quote the Robert Frost poem, Fire and Ice, uttering the words

Some say the world will end in fire;
Some say in ice.

This is typically a reference to the question of whether the universe will recollapse, forcing all its contents into smaller and smaller volumes, increasing the pressure and the temperature, or whether it will expand forever, gradually cooling to ever lower extremes of temperature. http://Louis-j-sheehan.com What is less often discussed however, is a related question concerning the very early cosmos - was the universe born in fire or in ice?

If you’re reading Cosmic Variance, chances are you’re aware of and comfortable with the idea of the big bang. Physicists arrive at this concept by first making observations of the universe today and understanding how these are described by well-established theories of gravity and particle physics. We then extrapolate back in time to infer what the early universe must have been like, and then test the theory by working out what new predictions result and checking whether they agree with observations. This methodology works remarkably well and has provided us with an extremely well tested, self-consistent and coherent understanding of the universe.

The central result that arises from this work is that the universe is expanding - all distant galaxies are moving away from us and the further away they are, the faster they are moving. Of course, this means that in the past all galaxies were closer together. When you get far enough back in time, what inevitably results is that one has a very high density of matter and, as your intuition from compressing everyday gases will tell you, one expects that in this early phase the universe should have been extremely hot - a birth in fire, in Frost’s language. In fact, this heat is what we see, diluted and reddened by cosmic expansion, as the cosmic microwave background radiation today.

The prediction and observation of this leftover radiation constitutes compelling evidence for big bang cosmology. However, it doesn’t answer the question of how all that hot matter came into being in the first place. Now, we do know that if we extrapolate far enough back in time one is eventually no longer able to use gravity (describing the physics of space and time and understood by Einstein’s General Relativity) and quantum mechanics (describing the physics of the very small) separately, but is forced to take into account their mutual effects. Thus, it is entirely possible that the origin of matter can only have its explanation in a theoretical framework that allows us to answer questions about gravity and particle physics working together in this way, such as string theory. However, we think we have an explanation that may be well-described within the theory of inflation, seemingly needed to solve the problems of homogeneity and flatness in the early universe, and thought to be responsible for the fluctuations in matter and spacetime that ultimately lead to large scale structure in the universe. Indeed, if inflation is correct, then its diluting power means that any preexisting mechanism for producing regular matter is rendered moot, and a new, post-inflationary mechanism is mandated. In Frost’s language, the universe may have been born in ice, and inflation may explain why, and how fire was breathed into this barren spacetime.http://Louis-j-sheehan.com

Inflation requires a large vacuum energy, due to the potential energy of a slowly-rolling scalar field, in order to cause the early universe to expand exponentially quickly. While this addresses the problems mentioned above, this accelerated expansion is also extremely efficient at diluting the universe of all other matter, leaving only the vacuum energy behind. Thus, within inflation, the question of the origin of the hot big bang becomes the question of how our huge universe, bereft of matter save for the potential energy of the inflaton and fleeting quantum fluctuations, is ultimately populated with the hot plasma of quantum fields that eventually cools to make galaxies, stars, planets, and you.

To get a handle on how this large vacuum energy can be converted into regular matter fields when inflation ends, it is useful to look at a caricature of an inflaton potential.

inflatonpot.jpg

As one can see, this consists of a remarkably flat portion, along which the inflaton slowly rolls, leading to inflation, followed by a piece where the field can pick up speed and cease to behave as a cosmological constant. It is this piece in which we will be interested. As the inflaton starts to oscillate rapidly around its minimum, there are two possible damping terms through which it can dissipate energy. One is natural redshifting due to the expansion of the universe. But the second is through decays to other particles. This can be quite an efficient process, and the energy density in the inflaton can be smoothly converted into that of a thermal bath of particles to which it couples. This process is known as reheating, and provides one possible way in which inflation can answer our question.

There is, however, a subtlety that can arise in this picture. The way I described it above, one pictures the decay of the inflaton as rather like a pendulum swinging in air, gradually transferring its energy to the air molecules through friction, and gradually coming to a halt. Indeed, this is a possibility, but it is not the only one. In fact, now that we’ve mentioned swinging, you might be able to imagine what else can happen. Anyone who has sat on a swing knows that if you are given a big push, and just sit on the swing, you will swing back and forth, and gradually come to a halt, as I described for the pendulum. However, one doesn’t have to be so passive, and every child knows that by kicking ones feet at just the right times, one can actually get the amplitude of the swing to grow larger and larger. This is a phenomenon that physicists call resonance.

How might this apply to the inflaton? Obviously, the inflaton doesn’t get to kick its feet - it has a natural frequency governed by the curvature of the potential, and roughly speaking that’s all there is to it. However, if one thinks in Fourier space, one can see that the equation governing how the inflaton decays into other matter fields depends on the wavelength (and therefore frequency) of those fields, or modes (it is, for you experts, a Mathieu equation). For a given inflaton potential, the natural frequency of the inflaton’s oscillations has no particular relationship to the frequency of a randomly chosen mode. However, there are certain ranges of mode frequencies for which the oscillations of the inflaton are just right to excite those modes resonantly, pumping lots of energy into them, just like the child on the swing. This is called parametric resonance, and for the case of the inflaton’s decay into matter, the whole process is referred to as preheating.http://Louis-j-sheehan.com

Although preheating is an out of equilibrium phenomenon, eventually almost all the energy produced equilibrates, and produces a plasma at a given equilibrium temperature. One might therefore wonder how there could be any observational consequences of this hypothesized early cosmic phase (and hence whether such considerations are scientific at all). But it turns out that some of the energy may never equilibrate, and that there are therefore a number of possible fascinating consequences of preheating. Some of these tightly constrain particle physics and inflationary models, others provide novel ways of approaching some unresolved cosmological conundrums. Next time I’ll tell you about them.

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Tuesday, November 18, 2008

enigma

Two new studies offer conflicting views of the effectiveness of mental-health services for children and teenagers.

In many health-care programs, clinicians who treat children's emotional and behavioral problems face mounting pressures to specify how much therapy kids really need.

Scant research has tracked youngsters receiving mental-health treatment outside universitybased programs. Two new studies, both published in the February Journal of the American Academy Of Child And Adolescent Psychiatry, venture into the real world of child mental-health services.

However, their clashing conclusions about what to expect from such treatment are sure to frustrate health-care insurers.

One investigation, directed by psychiatrist Adrian Angold of Duke University Medical Center in Durham, N.C., finds that seriously disturbed kids who attend at least eight sessions of psychotherapy or other mental-health care improve markedly and continue to progress as they get more treatment. The other study, led by psychologist Ana Regina Andrade of Vanderbilt University in Nashville, reveals comparable improvement in groups of children receiving either little or lots of psychotherapy.

Over 4 years, Angold's group conducted interviews and surveys with 1,422 children, ages 9 to 16, and their parents. Participants came from rural, largely low-income areas of North Carolina. As a large part of their sample, the researchers included children who, according to their parents, had behavior problems.

During the study, 365 children received some form of mental-health treatment. Most sought private psychotherapy or services at public mental-health centers. Kids who got such help had previously displayed more anxiety, depression, and problems in social and home life than untreated youngsters had. Symptoms had been worsening before they or their parents sought help. Eight or more treatment sessions lessened anxiety and depression, although many of the kids' other problems remained. Symptoms continued to recede as youngsters received more treatment. Those who attended fewer than eight sessions showed no improvement or, in some cases, got worse.

Andrade's team studied 568 youngsters who were having social and behavioral problems. These kids, ages 5 to 17, came from middle-class, military families. Each child was assessed at one of three military mental-health centers, where 531 kids then received at least one session of psychotherapy. http://louis_j_sheehan.today.com/

Most of the 568 children improved over the 1-year study. No differences emerged between those who received little or no psychotherapy and those who attended eight or more sessions.http://louis_j_sheehan.today.com/

Contrasts between the two studies—in kids' backgrounds and definitions of clinical improvement, for instance—virtually ensured different findings, says psychologist Kimberly Hoagwood of the National Institute of Mental Health in Bethesda, Md., in a comment published in the same journal.

Neither project tried to illuminate how specific therapeutic approaches worked for certain children, Hoagwood adds. This critical issue merits intensive research, in her view.

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Tuesday, November 11, 2008

meat 772.mea.00000 Louis J. Sheehan, Esquire

Louis J. Sheehan, Esquire. Buying local certainly reduces the miles food goes before we eat. But consumers aiming to shrink their ecological footprint will get more bang for their environmental buck by eating less red meat and dairy, reports a new study. The analysis finds that transporting food to the consumer accounts for only 4 percent of food-associated greenhouse gas emissions, while production contributes a hefty 83 percent. http://blogs.ebay.com/mytymouse1/home/_W0QQentrysyncidZ755826010

“There are many good reasons for going local,” comments Rich Pirog, associate director of the Leopold Center for Sustainable Agriculture at Iowa State University in Ames. “But this study is important. Food miles alone are not a reliable indicator of environmental impact.” http://blogs.ebay.com/mytymouse1/home/_W0QQentrysyncidZ755826010

For the average U.S. consumer, getting the equivalent of one-seventh of a week’s calories from chicken, fish or vegetables instead of red meat or dairy will do more to reduce greenhouse gas emissions than buying all local, all the time, the researchers say. Crunching the numbers revealed that delivery to the consumer accounts for only 1 percent of red meat–associated emissions. But the production path to red meat and dairy products is clouded with nitrous oxide and methane emissions, mainly from fertilizer use, manure management and animal digestion.

“Methane and nitrous oxide production are huge in agriculture,” says the study’s first author Christopher Weber of Carnegie Mellon University in Pittsburgh. These greenhouses gases are often left out of similar analyses, which have tended to focus solely on carbon or energy use. “That misses a huge part of the picture,” Weber says.

Weber, who conducted the study with colleague, H. Scott Matthews, notes that they aren’t trying to downplay the benefits of buying local. “I shop locally,” he says. “But there’s been so much emphasis on food miles. We felt it was important to look at the whole life cycle.”

Using data from the U.S. departments of Commerce, Agriculture, Transportation and other sources, Weber and Matthews modeled the total greenhouse gas emissions generated in making and moving all sorts of foods from cereals to fish to cheese. The work, to appear in the May 15 Environmental Science & Technology, paints a broad brush, cautions Weber. Because the model uses Commerce Department data, the food categories are defined by Commerce Department food sectors. So while cheese and milk are considered separately, fruits and vegetables are put in the same category.

Apples and oranges aside, the paper “is an important contribution,” comments Greg Keoleian of the Center for Sustainable Systems at the University of Michigan in Ann Arbor. “More quantitative assessments like this are needed to help us understand the consequences of our choices.”

The research highlights how complicated those choices are. “There is no one silver bullet way of reducing climate change,” says the Leopold Center’s Pirog. “These are very complex systems.” He notes that the environmental burden of food goes beyond emissions — fertilizers often impact water quality, for example. And while land use may not be as efficient on a small local farm, if that farm’s beef cattle are eating grass, they may have a lot less environmental baggage than corn-fed cattle from a conventional feedlot. Other choices, such as purchasing heirloom tomatoes, are important for maintaining crop diversity, which makes the agricultural sector less susceptible to diseases and pathogens.

Weber and Matthews’ analysis looks at the hard numbers of getting food to the plate, and paying attention to that path has merit, says Keoleian. But Americans would do well to make those paths less traveled, period, he says. A 2003 study Keoleian conducted with University of Michigan colleague Martin Heller found that 26 percent of edible food in the United States is wasted, uneaten on the plate or left as offerings to the mold gods in the back of the fridge. Upgrading appliances, like refrigerators, can also substantially reduce food-related energy consumption, he says. Louis J. Sheehan, Esquire

If there’s a take-home message, it might be that one-dimensional food choices aren’t very effective, Weber says. Pirog agrees. “As we look at food purchases we need to consider health, safety, the environment, economics and community,” Pirog says.

Overwhelmed? Don’t be. This new study just reemphasizes the sound advice people have been getting since elementary school, Pirog says. “Eat a healthy balanced diet, with a minimum of processed food. Eat a moderate amount of dairy and meat. Eat more whole grains and veggies. Following that advice will probably reduce your carbon footprint.”

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