The to-l ratio between powdered cocaine and crack cocaine was used as a guideline for minimal mandatory punishment. For instance, a minimum penalty of 5 years was administered for 5 grams of crack cocaine or grams of powdered cocaine. The War on Drugs resulted in an immense growth in court caseloads and the prison population. The War on Drugs focused on small-time drug dealers, who were generally poor young black males from the inner city.
Ultimately, the prison population doubled due to the arrest of drug dealers and their customers. By , that statistic had increased to nearly one in three. Although the consequences of crack cocaine today are not as substantial as they were during the early s, there still is a crusade against the effects of crack cocaine as it continues to plague communities around the world. We welcome suggested improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind. Your contribution may be further edited by our staff, and its publication is subject to our final approval.
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OTHER WORDS FROM crack
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Crack cocaine Crack cocaine is highly addictive and is produced by the conversion of cocaine, a fine white crystallized powder substance, into a smokable form that could be sold in smaller portions but distributed to more people. Start your free trial today for unlimited access to Britannica. Learn More in these related Britannica articles: War on Drugs. The U. Hypertension , condition that arises when the blood pressure is abnormally high.
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Paranoia , the central theme of a group of psychotic disorders characterized by systematic delusions and of the nonpsychotic paranoid personality disorder. The word paranoia was used by the ancient Greeks, apparently in much the same sense as the modern popular term insanity.
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Repairing Concrete Cracks Using Epoxy
Thank You for Your Contribution! Uh Oh. There was a problem with your submission. Please try again later. Acrylics, polycarbonate, polystyrene, styrene—acrylonitrile SAN , polysulfone, acrylonitrile—butadiene—styrene ABS , and polyphenylene oxide are most prone to stress cracking. Esters, ketones, and aromatic hydrocarbons are the solvents most likely to cause stress cracking [14—16].
These conditions produce small cracks in the plastic; when liquid adhesive is applied, it can penetrate the part, increasing the damage. The crack may eventually propagate through the entire part, causing part failure. A minimum of adhesive should be used, and excess adhesive should be immediately cleaned up. Anaerobic thread-locking adhesives should not be used with plastics that are prone to stress cracking.
Stresses induced by the threads in addition to stress from uncured adhesive outside the joint produce very high stress levels in the part. Surface preparation methods to alleviate stress cracking include abrading the surface with sandpaper, cleaning with isopropyl alcohol, and assembling the parts immediately after application of alcohol [14,15,17].
The use of an incompatible adhesive for the substrates can produce stress cracks. The part surface softens and weakens, creating a crack. Joining materials with different coefficients of thermal expansion can produce stress cracking when the part is subjected to high or low temperatures. Plastics expand at high temperatures and contract at low temperatures to different amounts, depending on their coefficients of thermal expansion.
If the plastics have different coefficients of thermal expansion, stresses are produced, which lower the strength of the joint. Coefficients of thermal expansion can be decreased by adding fillers or reinforcements or by increasing the amount of cross-linking. If material selections cannot be modified, thicker bond lines and more flexible adhesives can help reduce problems with stress cracking; however, the adhesive film cannot restrain large relative motions of parts [14—16]. Chemical attack of uncured UV-curable adhesives produced stress cracking in medical grade polycarbonate.
In solvent bonding of hollow articles, stress cracking can result if enclosed areas are not vented [18,19]. In solvent bonding, plasticizer migration from a less rigid substrate, such as flexible PVC, to a more rigid substrate can result in stress cracking and crazing, depending on the solvents and combination of substrates used in bonding. Plasticizer migration will occur after a plasticizer-free surface has been obtained.
The most satisfactory adhesives for PVC are the acrylates, epoxies, urethanes, and hot melts . Generally, the more polar plastics require more polar solvents. Figure 9. With increasing values, however, anomalies become apparent. The discrepancy can be attributed, at least in part, to differences in crystallinity, the presence of compounding ingredients, and differences in chemical composition of the bulk polymer from the surface. Surface treatment of polyethylene may have a strong effect in that polymer. Where solubility parameters and contact-angle measurements disagree, the latter provides the better direction for choosing adhesives, provided they have been carried out on the materials as they are actually prepared for bonding [4,7].
Critical surface tension versus solubility parameter of thermoplastics .
A good source for solubility parameters of a wide range of materials has been published by CRC Press . Thermosets, acetals, polyphenylene sulfide, polyolefins, polyamide, rigid polyvinyl chloride PVC , and polyethylene and polybutylene terephthalate are resistant to stress cracking. Acrylics, polycarbonate, polystyrene, styrene-acrylonitrile, polysulfone, acrylonitrile-butadiene-styrene ABS , and polyphenylene oxide are most prone to stress cracking.
Esters, ketones, and aromatic hydrocarbons are the solvents most likely to cause stress cracking. These conditions produce small cracks in the plastic; when liquid adhesive is applied, it can penetrate the part, aggravating the damage. Surface preparation methods to alleviate stress cracking include abrading the surface with sandpaper, cleaning with isopropyl alcohol, and assembling the parts immediately after application of alcohol. Plastics expand at high temperatures and contract at low temperatures by different amounts, depending on their coefficients of thermal expansion.
In solvent bonding of hollow articles, stress cracking can result if enclosed areas are not vented. The most satisfactory adhesives for PVC are the acrylates, epoxies, urethanes, and hot melts. Where solubility parameters and contact-angle measurements disagree, the latter provides the better direction for choosing adhesives, provided they have been carried out on the materials as they are actually prepared for bonding. Critical surface tension vs. A good source for solubility parameters of a wide range of materials has been published by CRC Press.
The cracks in this study are classified into two types: external cracks and internal cracks.