Physics in a New Era An Overview (2001) / Chapter Skim
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2. Complex Systems
2. Complex Systems
Pages 37-54
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From page 37... ...
Who can cleny, for instance, the desirability of understanding crack formation in structural materials, forecasting catastrophes such as earthquakes, or treating plaque deposition in arteries? A traditional approach in physics when trying to understand a system made up of many interacting parts is to break the system into smaller parts and study the behavior of each.
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From page 38... ...
Although materials in thermal equilibrium can display formidable complexity, nonequilibrium systems can behave in ways fundamentally different from equilibrium ones. Nature is filled with nonequilibrium systems: Looking out a window reveals much that is not in thermal equilibrium, including all living things.
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From page 39... ...
The glass phase has a clisorclerecl structure superficially similar to a liquid, but unlike the liquid phase, its molecules are frozen in place. Glasses have important properties that can be quite different from those of a crystal made of the same moleculesproperties, for example, that are vital to their use as optical fibers.
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From page 40... ...
Recent advances in computation and visualization techniques are now providing important new insight into this interplay through numerical simulation. Foams and Emulsions Foams and emulsions are mixtures of two different phases, often with a surfactant (for instance, a layer of soap)
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From page 41... ...
Improved computational capabilities enable not just theoretical modeling of unprecedented faithfulness, complexity, and size, but also the analysis of images made by video microscopy, yielding new insight into the motion and interactions of colloidal particles. The combination of advanced experimental probes, powerful computational resources, and new theoretical concepts is leading to a new level of understanding of nonequilibrium materials.
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From page 42... ...
This graph of data from the Tokamak Fusion Test Reactor at the Princeton Plasma Physics Laboratory, which achieved 10 MW of fusion power in 1994, shows how suppressing the turbulence can significantly boost the central plasma pressure and thus the fusion reaction rate.
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From page 43... ...
Turbulence in the solar corona, for example, appears to form extremely thin sheets of electric current, which may heat the solar corona. In fusion devices, plasma turbulence has been found theoretically and experimentally to generate large-scale sheared flows, which suppress turbulence and decrease thermal losses from the plasma.
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From page 44... ...
The picture at the right shows the magnetic field lines in a computer simulation of this process. Where the line is blue it is pointing inward and where it is gold it is pointing outward.
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From page 45... ...
The NIF will also study the interaction of intense x rays and matter and the subsequent shock-wave generation. These topics are also being studied at the Sandia National Laboratories using x rays proclucecl by dense plasma discharges.
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From page 46... ...
Understancling how proteins assume their correct shape remains a central problem in biophysics (see sidebar "Protein Folding". Biomechanics Cells depend on molecular motors for a variety of functions, such as cell division, material transport, and motion of all or part of the organism (like the beating of the heart or the movement of a limb)
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From page 47... ...
Even though the power of currently delivered supercomputers is little more than 1 teraflop (10~2 operations per second) , computers with petaflop power for tasks such as protein folding are anticipated in the near future by exploiting the latest silicon technology together with new ideas in computer design.
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From page 48... ...
In recent years researchers have measured the forces generated by a single motor cycle and the size of the elementary mechanical step. This research has required the invention of new kinds of equipment, such as optical tweezers, that permit precise manipulation of single bacterial cells as well as novel techniques for measu ri ng movements that are too smal I to see with an ord i nary m icroscope.
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From page 49... ...
but a rather complicated one in that channels exhibit great specificity for the ions permitted to permeate. Some channel types will allow the passage of sodium ions but exclude potassium and calcium ions, whereas others allow potassium or calcium ions to pass.
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From page 50... ...
This is the goal of channel biophysics in the early part of the 21st century. The end result will be an understanding, in atomic detail, of how neurons produce the nerve impulses that carry information in our own very complex computer, the brain.
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From page 51... ...
Earthquakes are becoming more expensive with each year, not because they are happening more often but because of the increased population density in our cities. An earthquake on the Wasatch fault in Utah would have had little effect on the agrarian society in 1901; in 2001, a bustling Salt Lake City sprawls along the same fault scarp that raised the mountains that overlook it.
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From page 52... ...
Several active faults of varying orientations typically absorb the motion of any given region, raising mountains and opening basins as they move. Modeling suggests that the lower continental crust flows, slowly deforming its shape, while sandwiched between a brittle, earthquake-prone upper crust and a stiff, yet still moving, mantle.
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From page 53... ...
As populations and expectations rise, uncertainties must be trimmed. Today's eruption forecasts use pattern recognition and logical, sometimes semiquantitative analysis of the processes that underlie the unrest, growing more precise and accurate.
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From page 54... ...
Recent advances in understanding this phenomenon have come from laboratory experiments, in situ observation, computer simulation, and theory. It appears that turbulent motion of the electrons facilitates the rapid changes in the magnetic field but just how this occurs is not yet fully understood.
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