U.S. President Barack Obama

Washington D.C. – April 20, 2012, President Obama signs a proclamation in the Oval Office of the White House, Mustique, Grenadines of St. Vincent, sheet of one stamp. The President Obama International Stamp Collection

Barack Obama, 44th President of the United States

Change doesn\u27t come from Washington. Change comes to Washington, Union, Grenadines of St. Vincent, Sheet of 6 stamps. The President Obama International Stamp Collection. No date given

Design, fabrication and performance evaluation of a 22-channel direct reading atomic emission spectrometer using inductively coupled plasma as a source of excitation

The indigenous design, fabrication and performance evaluation of a polychromator, using inductively coupled plasma (ICP) as a source of excitation, are described. A concave holographic grating is used as the dispersing element and a Paschen-Runge mount is chosen to focus the spectra over a wide range along the Rowland circle. Twenty-two exit slits, mounted along the circle, precisely correspond to the wavelengths used for determination of up to twenty elements present in the plasma. Radiations emerging from the exit slits are detected by photomultiplier tubes placed behind them. The photomultiplier signal is recorded by an electronic system consisting of an integrator and a PC-based data acquisition system. The performance of the spectrometer has been evaluated with an ICP excitation source. Synthetic standards in deionized water containing a mixture of twenty impurities have been analysed. Typical determination limits observed for elements range from sub-ppm to ppm levels. All the elements present as impurities can be detected simultaneously. It is also observed that each element has a different emitting region in the ICP flame for which the maximum signal to the background is obtained. The determination limits obtained corresponding to these zones are the lowest. A study of the sensitive emitting zones for several elements has been carried out and the results are demonstrated by photographs of the ICP flame. The study will help in achieving the minimum value of determination limit for an impurity element

President Obama Visits South America

Canouan, Grenadines of St. Vincent, sheet of 3 stamps. The President Obama International Stamp Collection. No date given

U.S. President Barack Obama, Portland, OR

U.S. President Barack Obama speaks at a campaign fundraiser at the Oregon Convention Center , Mustique, sheet of 4 stamps, The President Obama International Stamp Collection

September 11th Memorial, President Barack Obama Visits New York City

Bequia Grenadines of St. Vincent, sheet of 4 stamps, The President Obama International Stamp Collection. No date given

President Obama Visits Ireland

Mustique, Grenadines of St. Vincent, sheet of 4 stamps. The President Obama International Stamp Collection. No date given

Obama, 44th President of the United States

Change has come to America, Mayreau, sheet of 4 stamps, The President Obama International Stamp Collection. No date given