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Crack ((TOP))

In their analysis, now in the on-line edition of Drug and Alcohol Dependence, crack users were at higher risk than powder cocaine users for reporting a lifetime arrest or multiple recent arrests. Racial minorities were at low risk for powder cocaine use, but they tended to be at high risk for crack use.


Dr. Palamar and his team noted that individuals with higher education, higher income or full-time employment were much less likely to use crack; however, these were sometimes risk factors for powder cocaine use, which is often more associated with affluence. The researchers found that blacks were in fact at increased risk for lifetime and recent crack use, but not when controlling for other socioeconomic variables. However, blacks who did use either powder cocaine or crack tended to use at higher frequencies, possibly placing them at even higher risk for arrest.

The research study confirms that crack tends to be used by a more marginalized segment of society, and it is this socioeconomically disadvantaged segment of society who is at higher risk for arrest and subject to the 18:1 sentencing disparity. Since black individuals in the US are so much more likely to live in poverty, disproportionate numbers have been incarcerated for crack offenses, while more educated and affluent individuals are less likely to be subject to legal consequences for powder cocaine use.

The Fair Sentencing Act (2010) reduced sentencing disparities to 18:1, but sentencing disparities remain and the law is not retroactive, thus, those arrested prior to enactment remain in prison. The Smarter Sentencing Act (2014) was recently proposed to create less costly minimum terms for nonviolent drug offenders and would allow for the 8,800 federal prisoners (87% of whom are black) imprisoned for crack offenses to be resentenced in accordance with the Fair Sentencing Act.

The chart above shows recent trends in a single product crack spread, or the difference between the U.S. Gulf Coast conventional gasoline spot price (the black line) and the Louisiana Light Sweet crude spot price (the blue line). Crack spreads can be positive (the grey shaded region) or negative (the red shaded region), depending on relative product prices.

By comparing the price of crude oil (which is set in a global marketplace) with the price of refined products (which can be affected by local and seasonal factors), crack spreads can often give an indication of supply conditions in a given market.

(July 2022) In fiscal year 2021, there were 1,088 crack cocaine trafficking offenders, who accounted for 6.2% of all offenders sentenced for a drug trafficking offense. Crack cocaine trafficking offenders have decreased by 32.0% since fiscal year 2017.

The Crack Garden took a giant concrete slab that served as a central gathering area and created a series of cracks filled with different plants. The project reinvigorates the area by creating permeable space for plants to grow.

The cracks turn a barren, lifeless space into one that provides food for homeowners and a pleasant space for relaxing. From certain vantage points the lines of plantings stack up to present a more densely planted experience.

Crack sealing is used for active cracks in asphalt pavements so that water is kept out of the pavements. Sealant installation is affected by a number of factors including: humidity, rout size, crack preparation method, heating time, sealant finishing and protection, and the temperature of air, sealant and pavement.

Pennington, on his way back to Michigan Tech from a conference, decided to investigate. Still in his business clothes, he used a pad of paper from the hotel, used his phone to gather GPS data and paced off measurements in his dress shoes. The crack was 361 feet long, up to two feet wide and as deep as four or five feet in some spots. But what struck him most was the 6-foot high ridge beneath the crack; it had appeared at the same time as the crack.

In broken rock, sound travels faster as it moves parallel to cracks in the rock, and slower when it moves perpendicular to the cracks and has to travel across the fractures. The scientists found a pattern of refraction speeds that seemed to be consistent with the intense bending and then fracturing of the brittle limestone of a pop-up feature.

Crack formation is a frequent result of residual stress release from colloidal films made by the evaporation of colloidal droplets containing nanoparticles. Crack prevention is a significant task in industrial applications such as painting and inkjet printing with colloidal nanoparticles. Here, we illustrate how colloidal drops evaporate and how crack generation is dependent on the particle size and initial volume fraction, through direct visualization of the individual colloids with confocal laser microscopy. To prevent crack formation, we suggest use of a versatile method to control the colloid-polymer interactions by mixing a nonadsorbing polymer with the colloidal suspension, which is known to drive gelation of the particles with short-range attraction. Gelation-driven crack prevention is a feasible and simple method to obtain crack-free, uniform coatings through drying-mediated assembly of colloidal nanoparticles.

Colloidal suspensions, where colloids or nanoparticles are uniformly suspended in a solvent, are widely used in industry. A drying process is usually adopted to deposit the colloids on a solid surface, allowing fabrication of thin colloidal films1. Drying-mediated assembly of colloidal nanoparticles2 is a cutting-edge technology. However, cracking of the dried colloidal films frequently takes place, particularly for those made from nanoparticle suspensions3,4,5,6,7,8,9,10,11,12, which can thus cause critical problems for application. Prevention of cracking is a significant task to improve the quality of colloidal films containing nanoparticles13,14, as well as to increase the applicability of large-area, highly ordered and crack-free colloidal films15.

A variety of feasible methods for crack prevention have been suggested to date. For example, avoidance of cracking had been achieved through use of subsequent depositions of thin crack-free nanoparticle layers13, addition of hydrogels to suspensions to reduce their capillary pressures16, variation of the pH17 or addition of inorganic particles18 to control suspension flocculation, addition of a sol-gel glue19 or a sol-gel precursor15, addition of emulsion droplets to modulate suspension viscosity14 and use of organic colloids20 to enhance the fracture resistance of sol-gel coatings. Some examples of polymer addition for prevention of cracks can also be found in ceramic materials (for review, see21): polymers are added as binders into clays to increase fracture resistance22, which is an industrial tradition23, while poly(vinylalchohol) was found to reduce cracking in colloidal alumina24 and a variety of soft components, including polymers, soft spheres and glycerol, were reported to increase fracture resistance in mixtures with colloids25. However, despite the many attempts which have been made to prevent cracking, a simple and highly versatile method that utilizes well-known and well-controlled physics, such as gelation, is still required to allow more effective elimination of cracking in various colloidal suspensions.

The direct visualization of individual colloids inside drying colloidal drops would be helpful to uncover the details of crack formation for use in prevention. Herein, confocal laser microscopy was utilized to directly visualize the colloids during evaporation. By differences in contrast among the colloid, liquid, air and their mixture29, how cracks are generated during evaporation can be determined, with examination of the dependency on particle size and initial volume fraction. As a versatile method for crack prevention, we attempted to drive gelation through addition of a nonadsorbing polymer to the colloidal suspension, following the previously developed method30. The results demonstrated that this approach driving weak gelation with short-range attraction30 is feasible for the fabrication of uniform, crack-free coatings from colloidal drops. This approach will likely be useful in the fabrication of uniform, crack-free colloidal films for applications associated with inkjet printing, paints, coatings and ceramics.

The three evaporation stages could clearly be identified through confocal laser microscopy and use of fluorescent-dyed colloidal particles, as demonstrated in Fig. 1c. In particular, each stage was distinguishable owing to differences in the fluorescence intensities among the air, solvent and colloids. Confocal microscopy has widely been used for the direct observation of real-space motions of individual colloids29. A confocal laser microscope is a laser scanning optical microscope that utilizes a fluorescent technique36. With this approach, we are able to directly investigate crack initiation and growth dynamics. A similar approach was used in recent reports for crack studies14,37. Confocal microscopy is also useful for studies on evaporation gradients38, as well as on evaporative lithography39.

In conclusion, we demonstrated that cracking is an intrinsic and inevitable phenomenon for colloidal films made with hard sphere-like small colloids or nanoparticles (with radii at the nanoscale). We directly visualized the generation of cracks during evaporation of colloidal droplets using confocal laser microscopy and standard colloidal suspensions, with fluorescent-dyed colloids. From direct tracking of the individual colloids via confocal microscopy, we confirmed the critical effects of the particle size and initial concentration on crack formation. For versatile crack prevention, we demonstrated the gelation-mediated crack prevention that enabled us to obtain uniform, crack-free coatings through drying-mediated assembly of colloidal nanoparticles. This crack prevention method would be useful to obtain crack-free uniform colloidal films for inkjet printing, paints, coatings and ceramics. 350c69d7ab


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