In various criminal activities involving handwriting materials, they are closely related to paper. In the investigation of such criminal activities, the inspection of paper plays an important role. The inspection or identification of paper in forensic science is the same as the inspection of finished paper by the paper industry department. The reason is that the focus is different. Since the cases are various, the nature of different cases requires different levels of inspection or identification. The purpose of paper inspection in forensic science is to narrow the scope of investigation, provide clues to detect cases, point out directions, and provide a scientific basis for proving crime. Since the paper inspection materials provided in the case are limited, the unconventional microanalysis method is required in the inspection method. At present, many instrument analysis methods suitable for forensic science and technology have been developed, such as thin layer chromatography, high performance liquid chromatography, plasma emission spectroscopy, X-ray diffraction, etc. Thin layer chromatography The main component of paper is pulp, as well as a small amount of rubber, color and filler. As for the ingredients such as rubber, color and filler in paper, due to the different sources of raw materials used by various manufacturers, there are also differences in formulas and production processes. Therefore, the same kind of paper produced by different manufacturers must have certain differences in organic composition. This is the theoretical basis for our use of thin layer chromatography to test paper physical evidence. When testing paper by thin layer chromatography, generally use silica gel GF254 fluorescent thin layer plate, select the appropriate extractant for extraction (usually with ethanol), and then concentrate the extract for thin layer chromatography analysis. Commonly used developing agents are: V benzene: V methanol = 95:51 or V benzene: V methanol = 90: 5 If the TLC of the two paper samples is different, it can be determined that the two paper samples are different types of paper or the same type of paper produced by different manufacturers without contamination of the sample. If the TLC of the two paper samples is the same, it is generally the same kind of paper. Whether it is the paper produced by the same manufacturer, you need to use a TLC scanner. Determine the relative content of each component of the paper sample, or use other methods for further analysis. High performance liquid chromatography A part of the same kind of paper produced by different production places and different manufacturers not only has the same appearance, physical properties and fiber composition, but also other organic components are basically the same. It is difficult to distinguish and identify by general thin layer chromatography. But the relative content of the organic components of these papers is somewhat different. The use of high-performance liquid chromatography is an effective method to analyze the organic components such as pigments and gums in paper, and to determine the relative intensity of the main chromatographic peaks, which can further identify different manufacturers and batch numbers of the same paper. The use of high-performance liquid chromatography to test paper not only does not require the sample to be cracked, but also has a wide selection of mobile phases. A C18 reverse phase column was used for the analysis. The mobile phase was methanol / water or acetonitrile / water. The detector was an ultraviolet detector with a detection wavelength of 254 nm. The specific method is as follows: cut 5cm2 paper samples, and then cut into small pieces, add 1ml of absolute ethanol, soak for 10h, take the supernatant for chromatographic analysis. The experimental results show that the relative content of organic components of the same kind of paper from different manufacturers and different batches are different to varying degrees. Atomic emission spectrometry Atomic emission spectrometry is generally used to analyze the elemental composition of paper, especially the types and relative contents of metal elements in paper. Furthermore, the type of paper and the manufacturer can be distinguished. If you use ordinary atomic emission spectrometry, you need to mix the ashing of the paper sample with the carbon powder and put it in the electrode slot, and then excite the sample to measure the wavelength and intensity of the emitted line. Domestic commonly used Q24 medium-sized spectrograph and AC arc voltage. There are two specific methods of operation: the first method is to cut the paper into thin strips, and use a self-made spectral pure graphite tweezers to clamp one end of the paper strip. When an arc is formed between the electrodes, the other end is slowly sent to the gap of the graphite electrode to take a spectrum. The second method is to shred the paper sample and put it in a quartz crucible, ash it at 500 ° C in a muffle furnace, and then heat and dissolve it with 2mL 6M HCl. The solution was concentrated and added dropwise to a flat-tip electrode, which was pretreated with a 2% polystyrene benzene solution to prevent the sample solution from penetrating inside the electrode. After the sample solution evaporates to dryness on the electrode, take a spectrum. The second method has higher reproducibility of analysis. Development and fixing: use the red special hard type or ultraviolet type II dry plate produced by Tianjin Sensitive Film Factory, use developing solution D-11, develop for 5min (20 ℃), fix solution F5, fix for 20min (room temperature), and then wash with water. Analysis: The spectral line on the dry board is qualitatively determined according to the iron spectrum to determine the presence or absence of the element, and the relative content of each element is determined semi-quantitatively according to the blackness of the spectral line. Emission spectroscopy can measure dozens of elements in paper, but the constant elements are calcium, magnesium, aluminum, iron, and silicon, which reflect the characteristics of commonly used fillers in paper. When zinc oxide (ZnO) and barium sulfate (BaSO4) are used When used with titanium dioxide (TiO2) as filler, the content of zinc, barium and titanium is higher. In recent years, inductively coupled plasma emission spectroscopy has been used for paper analysis. Experiments show that the application of plasma emission spectroscopy can qualitatively and quantitatively analyze more than 20 common elements in paper to achieve the purpose of distinguishing similar papers. The specific operation method is as follows: take a 50cm2 paper sample, weigh it and cut it into small pieces, place it in a milled conical flask and soak it with 1ml of 10% HCl solution for 2h, then add 4ml of deionized water and place it for about 20h. Dilute to 10ml before testing. Each sample is tested three times and the average value is taken. Element content calculation and data analysis: After measuring the standard sample, the instrument can obtain a quantitative curve. After the paper test material and comparison sample are measured, the concentration value expressed in ppm is obtained, and then converted into a percentage content. Calcium, magnesium, aluminum, iron, silicon, potassium, and sodium are common elements in paper, and their percentages are all above 0.5%, while other elements are small or trace elements in paper. X-ray diffraction analysis A monochromatic X-ray incident on the crystal face of the sample can produce a diffraction pattern. The position and intensity of the diffraction line are closely related to the nature, composition and phase of the sample, and the intensity is proportional to its content. The inorganic fillers contained in the paper, such as talc, clay, titanium dioxide and magnesium sulfate, etc., can form their own diffraction lines. Due to the different manufacturing processes of different manufacturers, the sources of inorganic fillers used are different, and the varieties and quantities used are not completely the same. The crystal structure and relative content of the ingredients contained in them also differ. Therefore, the X-ray diffraction analysis method can be used to distinguish the same kind of paper produced by different manufacturers according to the position of the diffraction lines and the relative intensity between each other, and can further identify the paper patterns that are difficult to distinguish by other methods. When the conditions are ripe, the production time and production batch number can also be distinguished. X-ray diffraction analysis is a non-destructive test and can be performed directly on paper. The method for testing paper by this method is to use an automatic diffractometer, a copper target tube, a wavelength of 15418 × 10-14m, a target voltage of 40kV, a target current of 40mA, a continuous scanning interval of 3 ° to 60 °, and a scanning speed of 4 ° per minute. Cut the paper sample into 4cm2 and place it directly on the sample holder. The amount of filler to be tested can be as low as one thousandth. When analyzing unknowns, standard spectra can be used for searching. When paper inspection materials permit, it is necessary to adopt as many methods as possible to systematically analyze and inspect paper physical evidence. In this way, various test results can be complemented and verified, thereby improving the accuracy and reliability of the identification conclusion. Various inspection methods of paper have a certain scope of application, each with advantages and disadvantages. In actual work, it is necessary to formulate reasonable inspection procedures based on the specific conditions and inspection requirements of the inspection materials, as well as the existing equipment and experimental conditions. Normally, non-destructive testing is done first, followed by non-destructive testing. Due to the wide variety of papers, paper mills are spread all over the world, and the scope of use is large, the existing paper inspection methods generally cannot make the same conclusion, and can only identify the type of paper. In the case of comparison samples, the origin, brand and batch number can be determined; within a specific range, the same determination can be made. A floating shelf is a form of shelf with its wall fixings hidden within the shelf board, with no visible supporting brackets. It can be supported on hidden rods or bars that have been attached to studs. A thick floating shelf may be made of a hollow-core shelf glued to a cleat. 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A floating shelf may have two or more channels open from the back towards, but without reaching, the front, into which slide fasteners attached to the wall, typically held in place by screws inserted through the bottom of the shelf.
For typical floating shelf supports, a supplier suggests that floating brackets with a diameter of 12mm can support a shelf at least 22mm thick loaded with 20kg, and 18mm brackets can support 30kg on a 28mm shelf.
This description is in reference to one particular type of floating shelf support, others options are available. Also not to be confused with corner shelves, which would require entirely different supports to make them "float".
Floating shelves are a good fit for a contemporary minimalist style interior.They can be used to expand storage space, atop a radiator to double as storage, or inside a hallway to double as a console table.