Source: Laboratory of Alan Lester - University of Colorado Boulder
The physical properties of minerals include various measurable and discernible attributes, including color, streak, magnetic properties, hardness, crystal growth form, and crystal cleavage. These properties are mineral-specific, and they are fundamentally related to a particular mineral’s chemical make-up and atomic structure.
This video examines several physical properties that are useful in field and hand sample mineral identification— color, luster, streak, hardness, magnetism, and reaction with acid. Unlike crystal form and crystal cleavage, these properties are somewhat more closely linked to mineral chemical composition than to atomic structure, but both do play a role.
It is important to recognize that rocks are aggregates of mineral grains. Most rocks are polymineralic (multiple kinds of mineral grains) but some are effectively monomineralic (composed of a single mineral). Unlike crystal form and cleavage, which are terms reserved for mineral specimens, geologists might on occasion refer to a rock as having a general sort of color, hardness, magnetism, or reaction with acid. In other words, the physical properties looked at here are potentially appropriate for use with rocks as well as with specific minerals.…
1Department of Environmental Health Sciences, Johns Hopkins University Bloomberg School of Public Health, 2Department of International Health, Johns Hopkins University Bloomberg School of Public Health, 3Department of Medicine, Johns Hopkins University School of Medicine
1Sargent College, Boston University
Source: Laboratories of Jonas T. Kaplan and Sarah I. Gimbel—University of Southern California
The autonomic nervous system (ANS) controls the activity of the body's internal organs and regulates changes in their activity depending on the current environment. The vagus nerve, which innervates many of the internal organs, is an important part of the system. When our brain senses danger, vagal tone is inhibited, leading to a set of changes in the body designed to make us more prepared to fight or flee; for example, our heart rate increases, our pupils dilate, and we breath more quickly. Conversely, when the vagal system is activated, these physiological responses are inhibited, leading to a calmer state. The vagus nerve, then, acts as a kind of "brake" on our arousal. One interesting consequence of this calmer state is that it tends to promote social interaction-when we are not tensed and afraid of our immediate environment we are instead receptive to interacting with others. Poor functioning of this regulatory mechanism, therefore, may be associated with difficulties in social behavior.
One index of autonomic regulation is heart rate variability (HRV). HRV is a measure of how much the gap between one beat and the next varies over time. High HRV means there are continual fluctuations in the …
1Department of Mechanical Engineering, University of Michigan, 2Department of Biomedical Engineering, University of Michigan, 3Department of Biomedical Engineering, Institute for Cellular and Molecular Biology, The University of Texas at Austin, 4Department of Bioengineering, University of California, Berkeley, 5Physical Biosciences Division, Lawrence Berkeley National Laboratory
1Pneumococcal Research, Murdoch Childrens Research Institute, 2Department of Microbiology & Immunology, The University of Melbourne
Immunology and Infection
1Department of Hematology and Oncology, University of Göttingen, 2Institute of Neuropathology, University of Göttingen, 3Institute of Anatomy and Cellbiology, University of Halle
1Program in Neuroscience, Stony Brook University, 2Department of Pharmacological Sciences, Stony Brook University, 3Program in Molecular and Cellular Pharmacology, Stony Brook University
Immunology and Infection
1Department of Biological Science, Center for Colon Cancer Research, University of South Carolina, 2Department of Pathology, Chonnam National University Medical School
1Marsico Lung Institute/CF Center, University of North Carolina at Chapel Hill, 2Telethon Kids Institute, University of Western Australia, 3Department of Pediatrics, University of North Carolina at Chapel Hill
1Department of Physics, Lewis & Clark College, 2Program in Biochemistry and Molecular Biology, Lewis & Clark College, 3Jungers Center for Neuroscience Research, Oregon Health & Science University, 4Department of Chemistry, Lewis & Clark College
1Department of Molecular and Cellular Neuroscience, Nencki Institute of Experimental Biology, 2Department of Biochemistry, Nencki Institute of Experimental Biology, 3Neurobiology Centre, Nencki Institute of Experimental Biology
Source: Laboratory of Dr. B. Jill Venton - University of Virginia
Sample preparation is the way in which a sample is treated to prepare for analysis. Careful sample preparation is critical in analytical chemistry to accurately generate either a standard or unknown sample for a chemical measurement. Errors in analytical chemistry methods are categorized as random or systematic. Random errors are errors due to change and are often due to noise in instrument. Systematic errors are due to investigator or instrumental bias, which introduces an offset in the measured value. Errors in sample preparation are systematic errors, which will propagate through analysis, causing uncertainty or inaccuracies through improper calibration curves. Systematic errors can be eliminated through correct sample preparation and proper use of the instrument. Poor sample preparation can also sometimes cause harm to the instrument.…
Source: Laboratories of Dr. Ian Pepper and Dr. Charles Gerba - Arizona University
Demonstrating Author: Luisa Ikner
Traditional methods of analysis for microbial communities within soils have usually involved either cultural assays utilizing dilution and plating methodology on selective and differential media or direct count assays. Direct counts offer information about the total number of bacteria present, but give no information about the number or diversity of populations present within the community. Plate counts allow enumeration of total cultural or selected cultural populations, and hence provide information on the different populations present. However, since less than 1% of soil bacteria are readily culturable, cultural information offers only a piece of the picture. The actual fraction of the community that can be cultured depends on the medium chosen for cultural counts. Any single medium will select for the populations that are best suited to that particular medium.
In recent years, the advantages of studying community DNA extracted from soil samples have become apparent. This nonculture-based approach is thought to be more representative of the actual community present than culture-based approaches. In addition to providing information about the types of populations present, this …