Once upon a time, when I was older than five but no older than seven, I was sitting on a swing. I was in the moment and listening to the beat of the swing and the beat went on. Yes, the beat went on. As I sat and listened to the beat, I decided to change it. Maybe to something faster, maybe to something slower. I did not really care. Perhaps if I swung lower, it would go faster because I did not have as far to go between ends? So I swung lower and the beat went on. Yes, the beat went on. How about higher. The higher I go, the faster I go. I swung higher and the beat went on. Yes, the beat went on. I experimented more and more. Higher and higher as high as I could go. Lower and lower until the swinging was barely perceptible. And the beat went on.
And it is true. Given a weight and a length, a pendulum will keep the same time no mater how high or low it is swinging. There are subtleties. Pumping action is achieved by changing the weight a little bit in a way that changes the timing a little, but my equipment at the time was insufficiently accurate to detect this.
Sunday, January 10, 2016
Thursday, December 31, 2015
pancakes
Well, this did not get very far. I got hung up on some figures and it just dropped into the abyss. Ah well, now for an interlude, although none is really needed, of that most practical of home chemistry: cooking. I tend to have pancakes for breakfast and have been playing with variations for a nice, hardy style. Being a bit lazy, it comes from a mix. So, first I have to make the mix. This amount fits in a 1 liter jar.
2 cups flour
2/3 cups corn meal (somewhat finely ground)
1/3 cup ground flax seed
1/3 cup dried buttermilk (optional)
1/3 cup cashew meal
3 teaspoons baking powder
I suppose since they have corn meal they are actually flapjacks. Drop it all in the jar and give it a shake. Cashew meal is available from Trader Joes, but only seasonally. Unsalted raw cashews can be placed in a food processor for something a bit like it. Try to get it quite small. Counter-intuitively, they seem to make the pancakes a bit more fluffy in texture. (This has not been tested in any reasonably scientific manner.)
To use this mix for pancakes, use:
1 egg, beaten very, very well
2/3 cup mix
1/2 to 2/3 cup milk, depending on preference
It can be quite good to add fruit. I have added blueberries or a thin sliced tart apple or a banana. For bananas, it is not enough just to squish them a bit, but stir the result until it starts to look smooth.
Mix and place in a heated skillet, medium heat, and let cook until they start to set. This is when bubbles pop and the depression remains. Flip and cook until brown. Top with a favorite syrup and down while hot.
2 cups flour
2/3 cups corn meal (somewhat finely ground)
1/3 cup ground flax seed
1/3 cup dried buttermilk (optional)
1/3 cup cashew meal
3 teaspoons baking powder
I suppose since they have corn meal they are actually flapjacks. Drop it all in the jar and give it a shake. Cashew meal is available from Trader Joes, but only seasonally. Unsalted raw cashews can be placed in a food processor for something a bit like it. Try to get it quite small. Counter-intuitively, they seem to make the pancakes a bit more fluffy in texture. (This has not been tested in any reasonably scientific manner.)
To use this mix for pancakes, use:
1 egg, beaten very, very well
2/3 cup mix
1/2 to 2/3 cup milk, depending on preference
It can be quite good to add fruit. I have added blueberries or a thin sliced tart apple or a banana. For bananas, it is not enough just to squish them a bit, but stir the result until it starts to look smooth.
Mix and place in a heated skillet, medium heat, and let cook until they start to set. This is when bubbles pop and the depression remains. Flip and cook until brown. Top with a favorite syrup and down while hot.
Tuesday, June 10, 2014
Scanning Probe Microscopy (SPM)
Humans wish to explore the physical structure of ever smaller objects, as well as the very fine features of large objects. To this end, we invented microscopes to see better. However, there are fundamental limitations to the resolution of a microscope. Features smaller than half the wavelength (λ/2) of the light being used cannot be resolved. The wavelength can be shortened by placing the object to be observed within a material other than air or vacuum to buy a little more resolution, but it is not as much as can be desired. Using shorter wavelength light can increase resolution, but this light has more energy, eventually resulting in destruction of the sample and requiring different optics. Games can be played with uncertainty to increase resolution in one dimension while losing it in another using squeezed light. Eventually, the call for greater resolution leaves us blind and we must follow the example of the blind man and reach out and touch the object in order to see it.
Scanning probe microscopy (SPM) is the blanket term for technologies that take some sort of "finger" into close proximity of an object to be studied. This "finger" is kept at a set distance from the object using some sort of feedback and moved with respect to the object in order to explore its shape. The surface is mapped out, usually in a grid, in order to form the complete picture. Two main forms of SPM are scanning tunneling microscopy (STM) and atomic force microscopy (AFM).
The first, STM, uses a metal tip into close proximity of a conductive sample as the "finger", or tip, inside a vacuum. The tip can be as simple as a wire sliced so that it comes to a sharp point. When this is brought close to the sample, but not touching, the vacuum between the tip and the sample acts as an insulator preventing current from flowing. However, there is a finite probability of electrons tunneling across the gap resulting in a small current. The probability is sensitively dependent on the distance. To map out the surface, the surface is moved with respect to the tip and a feedback loop is used to maintain the tip at a constant distance over the surface. The vertical motion required to keep the current constant is recorded and used for the image. This is used to achieve atomic resolution and even observe subatomic structure such as orbitals. (This later is, of course, completely impossible.)
Variations on this theme are also used. Most simply, the sample can be scanned at a constant height while the changing current is recorded to produce the picture. One I have found particularly interesting is inelastic electron tunneling spectroscopy wherein electrons of very carefully controlled velocity (via controlling the energy) are used to reveal vibrational modes of chemisorbed species on a metallic surface.
The second, AFM, is more generalized as it does not require any specialized materials. The tip is often a microfabicated cantilever of some insulator which is placed close to or in contact with the surface. Placed in contact, the surface is moved around while the deflection of the cantilever is measured or the motion required to keep the deflection constant is measured, similarly to the two basic modes of using STM. The cantilever may also be operated in tapping mode, where the cantilever still comes into contact with the surface, but is not dragged along it. Even this can be destructive to the surface, so it may also be operated in non-contact mode. For this, the cantilever is vibrated at a resonant frequency and the amplitude of the vibration is monitored. When it comes close to the surface, the surface dampens the vibrations even without any contact, providing a measure.
Measurement of the deflection of the cantilever was initially done using an STM above the cantilever reasoning that this would be very sensitive to the position. This turned out to be surprisingly difficult and now a laser is usually reflected off the cantilever onto a photosensitive diode or array. Atomic resolution has been a much harder fight, but now can be achieved. The variations of AFM can seem endless. Changing the material of the tip or adding material to the tip changes the interaction between the tip and the surface. For instance, magnetic material may be added to the tip to image magnetic domains in a sample. Another variation places chemicals on the probe and measures chemical interactions.
Scanning probe microscopy (SPM) is the blanket term for technologies that take some sort of "finger" into close proximity of an object to be studied. This "finger" is kept at a set distance from the object using some sort of feedback and moved with respect to the object in order to explore its shape. The surface is mapped out, usually in a grid, in order to form the complete picture. Two main forms of SPM are scanning tunneling microscopy (STM) and atomic force microscopy (AFM).
 |
| Schematic of a scanning tunneling microscope. Probability of tunneling (P) is dependent on the distance between the surface and the tip (d) such that it falls off exponentially. |
The first, STM, uses a metal tip into close proximity of a conductive sample as the "finger", or tip, inside a vacuum. The tip can be as simple as a wire sliced so that it comes to a sharp point. When this is brought close to the sample, but not touching, the vacuum between the tip and the sample acts as an insulator preventing current from flowing. However, there is a finite probability of electrons tunneling across the gap resulting in a small current. The probability is sensitively dependent on the distance. To map out the surface, the surface is moved with respect to the tip and a feedback loop is used to maintain the tip at a constant distance over the surface. The vertical motion required to keep the current constant is recorded and used for the image. This is used to achieve atomic resolution and even observe subatomic structure such as orbitals. (This later is, of course, completely impossible.)
Variations on this theme are also used. Most simply, the sample can be scanned at a constant height while the changing current is recorded to produce the picture. One I have found particularly interesting is inelastic electron tunneling spectroscopy wherein electrons of very carefully controlled velocity (via controlling the energy) are used to reveal vibrational modes of chemisorbed species on a metallic surface.
 |
| Schematic of an atomic force microscope. |
Measurement of the deflection of the cantilever was initially done using an STM above the cantilever reasoning that this would be very sensitive to the position. This turned out to be surprisingly difficult and now a laser is usually reflected off the cantilever onto a photosensitive diode or array. Atomic resolution has been a much harder fight, but now can be achieved. The variations of AFM can seem endless. Changing the material of the tip or adding material to the tip changes the interaction between the tip and the surface. For instance, magnetic material may be added to the tip to image magnetic domains in a sample. Another variation places chemicals on the probe and measures chemical interactions.
Sunday, April 20, 2014
The point
I'm sure this will evolve over time, but here is my aim with this blog:
I will attempt to write about interesting items I have read about in a way that is accessible to a knowledgeable public. For the most part, these will not contain overview, but will refer back to posts that should provide overview. I am not a science writer nor have I aspired to be a science writer, but this seems like the thing to do at the moment. I will probably miss some background that is needed, in which case I may have to do background posts after a post as well as before. I will not cover high school level science, I expect a knowledgeable public to know that already.
The title of the blog really just says who I am. I worked with physical chemists as an undergraduate doing scanning probe microscopy. (I'll write an overview about that soon.) I was in chemical physics (part of the chemistry department) as a graduate doing nuclear magnetic resonance. (That will be the next overview I write.) In both of these, I purchased very few chemicals and many people do confuse me with a physicist, but I must confess to being a chemist in actual fact. I have an interest in fuel cells and the proposals I wrote as part of my degree tended to revolve around these. (Yep, there will likely be an overview on that soon, too.) I will try to stretch to the more interesting subjects that others I have come into contact with have studied, such as the membrane proteins studied by Eduard Chekmenev.
So, there will be two types of post: overview and detail. Hopefully there will be an overview post to introduce each subject of detail. Hiking is already covered quite well in one of my other blogs.
I will attempt to write about interesting items I have read about in a way that is accessible to a knowledgeable public. For the most part, these will not contain overview, but will refer back to posts that should provide overview. I am not a science writer nor have I aspired to be a science writer, but this seems like the thing to do at the moment. I will probably miss some background that is needed, in which case I may have to do background posts after a post as well as before. I will not cover high school level science, I expect a knowledgeable public to know that already.
The title of the blog really just says who I am. I worked with physical chemists as an undergraduate doing scanning probe microscopy. (I'll write an overview about that soon.) I was in chemical physics (part of the chemistry department) as a graduate doing nuclear magnetic resonance. (That will be the next overview I write.) In both of these, I purchased very few chemicals and many people do confuse me with a physicist, but I must confess to being a chemist in actual fact. I have an interest in fuel cells and the proposals I wrote as part of my degree tended to revolve around these. (Yep, there will likely be an overview on that soon, too.) I will try to stretch to the more interesting subjects that others I have come into contact with have studied, such as the membrane proteins studied by Eduard Chekmenev.
So, there will be two types of post: overview and detail. Hopefully there will be an overview post to introduce each subject of detail. Hiking is already covered quite well in one of my other blogs.
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