Electron-electron angular correlation experiments, or so-called (e,2e) coincidence experiments, provide the most detailed test of theories which attempt to describe the ionisation of a target atom by an incoming electron.
The parameters (Ea,qa,fa,Eb,qb,fb) are freely selectable experimentally within the constraints that energy and momentum must be conserved during the collision. In the experiments described here the DCS has been measured in the perpendicular plane using a helium target with incident electron energies ranging from 10eV to 80eV above the ionisation threshold. The electron coincidence spectrometer was designed to measure angular and energy correlations between low energy electrons emerging from near-threshold electron impact ionisation of helium and is capable of accessing all geometries from the perpendicular plane to coplanar geometry. A number of modifications to the original spectrometer as described in Hawley-Jones et al (1992) have been implemented and are detailed elsewhere. Unique to this (e,2e) electron spectrometer is the computer interface which controls and optimises the spectrometer during normal operation.
Figure 2 is a block diagram of the hardware interface between the computer and the spectrometer. At the heart of the operation is an IBM 80286 PC which controls the spectrometer and receives information about the system status from monitors around the spectrometer. The electrostatic lens and deflector voltages in the system are supplied by separate optically isolated active supplies controlled by 12A bit digital to analogue converter (DAC) cards, while a digital monitor measures the voltages and currents on the various lens and deflector elements around the system. The analyser positions are measured by potentiometers located in the drive shafts external to the spectrometer, and are monitored by a datalogger located on the main PC bus, which also monitors the EHT supplies and the vacuum pressure in the system. Count rates from the channel electron multipliers and photomultiplier tube are monitored by a 32 bit counter board, and the TAC output is sent directly to an MCA card installed in the main PC.
The software controlling the electron coincidence spectrometer is written to address specific tasks unique to the coincidence experiment. The main PC controls the spectrometer lens and deflector tuning during operation, optimising these voltages using a Simplex method.
Following input of relevant control information, the system is switched to computer control. The electron gun is then optimised to the counts detected by the photomultiplier tube, thus ensuring that the electron current is focussed to a beam of diameter approximately 1mm at the gas jet. The analyser input lenses and deflectors are then adjusted by the computer to optimise the non-coincidence counting rate of each analyser. A coincidence correlation spectrum is then acquired for a predetermined time, after which the analysers are moved to a new position and the optimisation procedure repeated in the inner loop.
Once the analysers have moved around the detection plane, the whole system is reoptimised and the process of data collection repeated. A correlation function between the scattered and ejected electrons is therefore accumulated over many sweeps of the detection plane until the results are statistically significant.
During operation the running conditions are monitored every 50 seconds by the data logger, allowing any anomalies in the data to be accounted for when final results are considered. Results from experiment for the symmetric case, where the outgoing electrons following the collision have equal energy, are shown in the figures 4a - 4h. In the perpendicular plane, the symmetry about the incident electron beam direction requires that the DCS must be symmetric about f = 180A° and this is evident in the data.
Inspection of the 94.6eV data (35eV scattered and ejected electron energies) indicates that this result does not follow the trends of the other data in the set.
The resolution of the spectrometer (~ 1eV) does not allow these contributions to be excluded, and so the 94.6eV data set cannot strictly be considered as part of the overall set of data which is presented here.
The first result in this data set therefore is the same as the first result in the previous set, allowing a convenient point for common normalisation of the data sets.
Above 54.6eV incident energy the results differ markedly, the angular correlation evolving into a single broad peak instead of the three distinct peaks observed in the symmetric case.
This is most clearly evident at 74.6eV incident energy, where the symmetric case shows three distinct peaks of approximately equal intensity, whereas the non-symmetric case shows only a broad featureless structure centred about 180A°.
The sets of data shown in figures 4 and 5 were each normalised relative to the result obtained at 34.6eV incident energy, where both the electrons emerge from the interaction region with an energy of 5eV. The relative angular data presented at any particular energy is normalised by consideration of the electron singles counting rate, which depends on the Double Differential Cross Section at 90A° but is independent of the azimuthal angle f. The procedure adopted here allows an upper and lower bound to be estimated, as no facility exists to allow these overlap volumes to be accurately determined experimentally as is implemented by other electron scattering groups. The DDCS gives the probability of obtaining an electron from the scattering event at an angle q1 in a solid angle dW1 at an energy E1 A± dE1.
The solid angle of detection depends upon the geometry and operating potentials of the electrostatic lenses, and is therefore also a function of the detected electron energy.
VA(E1) is given by the three way overlap of the gas beam, electron beam and volume as seen by the analyser. The DDCS varies only slowly over the energy range dE accepted by the analyser (Jones et al 1991) as does the efficiency and solid angle of detection of the analyser as determined from electrostatic lens studies. The energy resolution DEA is independent of E1 because the pass energy of the hemispherical deflector is kept constant. This expression can be rearranged to yield the ratios of analyser efficiency and solid angle in terms of the DDCS, singles count rates and overlap volumes at the two energies E1 and E2 for an incident energy Einc.. The ratios on the left-hand side of this equation were obtained from the DDCS data of MA?ller-Fiedler et al (1986) at an incident energy of 200eV for each analyser at the selected energies of interest. The first three terms in this expression are evaluated directly from the experiment, while the fourth and fifth terms are taken from the data of MA?ller-Fiedler et al (1986).
As no experimental facilities existed to measure these parameters, a SIMION ray-tracing model was set-up to allow a computational determination of these volumetric terms. The analyser input electrostatic lenses were also modelled to determine the volume viewed at the interaction point for the varying energies of electrons selected.
Figure 6 indicates the experimental geometry as viewed by the analysers in the perpendicular plane, where the atomic beam direction is at 45A° to the incident electron beam trajectory.
Table 1 indicates the calculated relationship GV as determined from the SIMION ray tracing model, and these values have been used to calculate the normalisations as given in figure 4. The dominant error in the expression is given by the double differential cross sections as measured by MA?ller-Fiedler et al (1986), since these terms arise four times in the expression, and typically have measurement errors of A± 15%. This is possible since the q = 90A° coplanar symmetric energy-sharing result is identical to the perpendicular plane f = 180A° energy-sharing result. Since data was not obtained at an incident energy of 100eV in these experiments, an interpolation between the energy normalised symmetric results yields a relative value. The uncertainty in the normalisations of the relative energy is approximately A±30%, as discussed in the previous section. The absolute differential cross sections as presented in figures 4 and 5 therefore have uncertainties of approximately A±44%. These latter calculations, normalised to one energy, produced results that were close to those of the experiment.


A simple descriptive model for the symmetric case illuminates a possible scattering processes involved. On the other hand the peak that is observed at 180A° can be explained in terms of either single or multiple scattering.
In terms of single scattering it is due to the incident electron selecting a bound electron whose momentum is equal in magnitude but opposite in direction to its own momentum. In terms of multiple scattering, particularly at the lower incident energies, the peak at 180A° has additional contributions that may be described by outgoing electron correlations as in the Wannier model.
The mass equivalence of the scattered and ejected electrons requires that a quasi-free collision results in electrons emerging at approximately 90A° to each other irrespective of their resulting energies, and so application of this model would once again yield three peaks, although the relative peak intensities might be expected to change. These results predict a single peak at 180A° due to a mechanism following elastic scattering of the incident electron from the nucleus that is more delicate and complex than the quasi-free collision, however the wings at the lower energies in the experiment are not predicted by this model. This may not be entirely unexpected as the DWBA model gives better results at higher energies. The central peak predicted by the theory also differs in width and height from the results presented here, when normalised to the 34.6eV data.
The first photograph (1826) - Joseph Niepce, a French inventor and pioneer in photography, is generally credited with producing the first photograph. Easy Peasy Fact:Following Niepcea€™s experiments, in 1829 Louis Daguerre stepped up to make some improvements on a novel idea.
Adafruit: The oldest street scene photos of New York City - Check out these incredible (and incredibly old) photos of NYC, via Ephemeral New York. The oldest street scene photos of New York CityCheck out these incredible (and incredibly old) photos of NYC, via Ephemeral New York. I still remember reading about Louis Daguerre's invention, the daguerreotype, in high school. The Making of the American Museum of Natural Historya€™s Wildlife DioramasFossil shark-jaw restoration, 1909.
Very old portrait of three men identified as (from left to right) Henry, George, and Stephen Childs, November 25, 1842. In 1840, Hippolyte Bayard, a pioneer of early photography, created an image called Self-Portrait as a Drowned Man. 10 Times History Was Captured in Living ColorColor photographs go back to before you might think.
Louis Daguerrea€™s view of the Boulevard du Temple in the French capital was captured in 1938, using a method a€“ the daguerreotype a€“ that took around seven minutes to develop a single image.Such a long exposure meant that anything moving around was not picked up.
Deben bi-axial tensile stages can be used for bi-axially stretching sheet material such as textiles, including leather, and also various polymers. The tensile stage allows engineers and scientists to study the effects of bi-axial force upon various materials.
These stages are made to order but we do have some standard designs, contact us with your requirements.
The content of this website (content being images, text, sound and video files, programs and scripts) of this website is copyright © Deben UK Limited unless specifically mentioned. Quadrupole mass spectrometers allow fast measurements within milliseconds and offer a high dynamic range from the ppb to the percentage level.
InProcess Instruments has specialized in a modular concept of quadrupole mass spectrometers for online gas analysis. These experiments measure the angular correlation between a projectile electron which is scattered from a target and a resulting electron which is ionised from the target. For an unpolarised target and unpolarised incident electron beam the only azimuthal angle of significance is given by f = fa - fb. When the electrons are detected in the perpendicular plane, the two angles qa and qb are both equal to 90A°. The perpendicular plane is accessed mainly through double collision processes (Hawley-Jones et al (1992), which represent only part of the full dynamical picture. The computer loads all the voltage supplies from either a manually selected set of voltages or from the results of a previous optimisation run.
This decouples the tuning of the electron gun from any tuning requirements of the electron analysers. This should be compared with the data obtained near threshold by Hawley-Jones et al (1992), which also shows a single peak with an approximately Gaussian structure.
This is considered to be due to the contribution to the cross section of a number of resonances in helium for scattered and ejected electron energies around 35eV. The model indicated that the electron gun operating at the voltages determined by the optimisation routines produced an electron beam of diameter approximately 1.0mm at the interaction region, consistent with the tuning of the electron beam onto counts from the photomultiplier which views a 1mm3 volume. For the non-symmetric data no compensation is required for volume effects since GV = 1.0 at all values of Ei. The electrons are then able to emerge at approximately 90A° with respect to each other in the perpendicular plane, as is observed.
As the momentum distribution of the bound electron peaks at zero for helium, the peak at 180A° diminishes with increased incident electron energy as the probability of finding a bound electron with the required momentum decreases. Niepcea€™s photograph shows a view from the Window at Le Gras, and it only took eight hours of exposure time!The history of photography has roots in remote antiquity with the discovery of the principle of the camera obscura and the observation that some substances are visibly altered by exposure to light.
Again employing the use of solvents and metal plates as a canvas, Daguerre utilized a combination of silver and iodine to make a surface more sensitive to light, thereby taking less time to develop. Half of the Limburg province of Belgium is added to the Netherlands, giving rise to a Belgian Limburg and Dutch Limburg (the latter being from September 5 joined to the German Confederation).June 3 a€“ Destruction of opium at Humen begins, casus belli for Britain to open the 3-year First Opium War against Qing dynasty China. Bayard had just perfected the process of printing on to paper, which would come to define photography in the following century, but the French government had decided to invest instead in the daguerrotype, a process invented by his rival, Louis Daguerre. The only figure to stay still long enough was a man, on the corner of the street, who had stopped to have his shoes shined.Created using a chemically-treated silver plate, it only shows anyone at all because the man stopped long enough to make history. Two axes move and the opposite axes track on slides, for a full four axes system consider our quad-axis testing solution.
We make systems with very high force (up to 100kN) or miniature systems for bio-medical applications. The stage has four independently controlled axes with separate motors, extensometers and loadcells. This stage is available as a standard or custom system, if you are interested please contact us with your exact requirements. Quadrupole mass spectrometers are the most widespread systems because they perform very well.
Further it allows the electron gun to be aligned and focussed accurately onto the interaction region whose centre is located at the intersection of the axes of rotation of the analysers and the electron gun. This type of double collision process must therefore be modelled using higher order scattering terms as is done using the DWBA. As far as is known, nobody thought of bringing these two phenomena together to capture camera images in permanent form until around 1800, when Thomas Wedgwood made the first reliably documented although unsuccessful attempt.


It didna€™t take long for others to seize the new technology and create daguerreotypes of New York City street scenes. Daguerreotypes are sharply defined, highly reflective, one-of-a-kind photographs on silver-coated copper plates, usually packaged behind glass and kept in protective cases.
This is essential for experiments where all of these may be varied over 3-Dimensional space.
The Government, which has been only too generous to Monsieur Daguerre, has said it can do nothing for Monsieur Bayard, and the poor wretch has drowned himself.
Chemistry student Robert Cornelius was so fascinated by the chemical process involved in Daguerrea€™s work that he sought to make some improvements himself.
It was commercially introduced in 1839, a date generally accepted as the birth year of practical photography.The metal-based daguerreotype process soon had some competition from the paper-based calotype negative and salt print processes invented by Henry Fox Talbot.
And in 1839 Cornelius shot a self-portrait daguerrotype that some historians believe was the first modern photograph of a man ever produced. For over two weeks in the summer of 2002, scientists and conservators at this prestigious facility subjected the artifact, its frame, and support materials to extensive and rigorous non-destructive testing. The result was a very complete scientific and technical analysis of the object, which in turn provided better criteria for its secure and permanent case design and presentation in the lobby of the newly-renovated Harry Ransom Center.The plate also received extensive attention from the photographic technicians at the Institute, who spent a day and a half with the original heliograph in their photographic studios in order to record photographically and digitally all aspects of the plate. The object was documented under all manner of scientific lights, including infrared and ultraviolet spectra. Long before the first photographs were made, Chinese philosopher Mo Ti and Greek mathematicians Aristotle and Euclid described a pinhole camera in the 5th and 4th centuries BCE. In the 6th century CE, Byzantine mathematician Anthemius of Tralles used a type of camera obscura in his experimentsIbn al-Haytham (Alhazen) (965 in Basra a€“ c. Wilhelm Homberg described how light darkened some chemicals (photochemical effect) in 1694. The novel Giphantie (by the French Tiphaigne de la Roche, 1729a€“74) described what could be interpreted as photography.Around the year 1800, Thomas Wedgwood made the first known attempt to capture the image in a camera obscura by means of a light-sensitive substance. As with the bitumen process, the result appeared as a positive when it was suitably lit and viewed. A strong hot solution of common salt served to stabilize or fix the image by removing the remaining silver iodide. On 7 January 1839, this first complete practical photographic process was announced at a meeting of the French Academy of Sciences, and the news quickly spread.
At first, all details of the process were withheld and specimens were shown only at Daguerre's studio, under his close supervision, to Academy members and other distinguished guests. Paper with a coating of silver iodide was exposed in the camera and developed into a translucent negative image. Unlike a daguerreotype, which could only be copied by rephotographing it with a camera, a calotype negative could be used to make a large number of positive prints by simple contact printing.
The calotype had yet another distinction compared to other early photographic processes, in that the finished product lacked fine clarity due to its translucent paper negative. This was seen as a positive attribute for portraits because it softened the appearance of the human face. Talbot patented this process,[20] which greatly limited its adoption, and spent many years pressing lawsuits against alleged infringers. He attempted to enforce a very broad interpretation of his patent, earning himself the ill will of photographers who were using the related glass-based processes later introduced by other inventors, but he was eventually defeated. Nonetheless, Talbot's developed-out silver halide negative process is the basic technology used by chemical film cameras today. Hippolyte Bayard had also developed a method of photography but delayed announcing it, and so was not recognized as its inventor.In 1839, John Herschel made the first glass negative, but his process was difficult to reproduce.
The new formula was sold by the Platinotype Company in London as Sulpho-Pyrogallol Developer.Nineteenth-century experimentation with photographic processes frequently became proprietary. This adaptation influenced the design of cameras for decades and is still found in use today in some professional cameras. Petersburg, Russia studio Levitsky would first propose the idea to artificially light subjects in a studio setting using electric lighting along with daylight.
In 1884 George Eastman, of Rochester, New York, developed dry gel on paper, or film, to replace the photographic plate so that a photographer no longer needed to carry boxes of plates and toxic chemicals around. Now anyone could take a photograph and leave the complex parts of the process to others, and photography became available for the mass-market in 1901 with the introduction of the Kodak Brownie.A practical means of color photography was sought from the very beginning.
Results were demonstrated by Edmond Becquerel as early as 1848, but exposures lasting for hours or days were required and the captured colors were so light-sensitive they would only bear very brief inspection in dim light.The first durable color photograph was a set of three black-and-white photographs taken through red, green and blue color filters and shown superimposed by using three projectors with similar filters. It was taken by Thomas Sutton in 1861 for use in a lecture by the Scottish physicist James Clerk Maxwell, who had proposed the method in 1855.[27] The photographic emulsions then in use were insensitive to most of the spectrum, so the result was very imperfect and the demonstration was soon forgotten. Maxwell's method is now most widely known through the early 20th century work of Sergei Prokudin-Gorskii. Included were methods for viewing a set of three color-filtered black-and-white photographs in color without having to project them, and for using them to make full-color prints on paper.[28]The first widely used method of color photography was the Autochrome plate, commercially introduced in 1907.
If the individual filter elements were small enough, the three primary colors would blend together in the eye and produce the same additive color synthesis as the filtered projection of three separate photographs.
Autochrome plates had an integral mosaic filter layer composed of millions of dyed potato starch grains. Reversal processing was used to develop each plate into a transparent positive that could be viewed directly or projected with an ordinary projector. The mosaic filter layer absorbed about 90 percent of the light passing through, so a long exposure was required and a bright projection or viewing light was desirable. Competing screen plate products soon appeared and film-based versions were eventually made.
A complex processing operation produced complementary cyan, magenta and yellow dye images in those layers, resulting in a subtractive color image.
Kirsch at the National Institute of Standards and Technology developed a binary digital version of an existing technology, the wirephoto drum scanner, so that alphanumeric characters, diagrams, photographs and other graphics could be transferred into digital computer memory. The lab was working on the Picturephone and on the development of semiconductor bubble memory.
The essence of the design was the ability to transfer charge along the surface of a semiconductor. Michael Tompsett from Bell Labs however, who discovered that the CCD could be used as an imaging sensor.



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