As commercial successors of governmental ASIC solutions have become available, also known as custom hardware attacks, two emerging technologies have proven their capability in the brute-force attack of certain ciphers. One is modern graphics processing unit (GPU) technology,[page needed] the other is the field-programmable gate array (FPGA) technology. GPUs benefit from their wide availability and price-performance benefit, FPGAs from their energy efficiency per cryptographic operation. Both technologies try to transport the benefits of parallel processing to brute-force attacks. In case of GPUs some hundreds, in the case of FPGA some thousand processing units making them much better suited to cracking passwords than conventional processors.Various publications in the fields of cryptographic analysis have proved the energy efficiency of today's FPGA technology, for example, the COPACOBANA FPGA Cluster computer consumes the same energy as a single PC (600 W), but performs like 2,500 PCs for certain algorithms. A number of firms provide hardware-based FPGA cryptographic analysis solutions from a single FPGA PCI Express card up to dedicated FPGA computers. WPA and WPA2 encryption have successfully been brute-force attacked by reducing the workload by a factor of 50 in comparison to conventional CPUs and some hundred in case of FPGAs.
If non-operative care is chosen, regular follow-up care for a physical exam and x-rays is important to ensure that the fracture stays in good position and heals appropriately. Cutting down or quitting smoking and tight blood sugar control if you are a diabetic is important for the healing process. One fall or continued lack of compliance with early walking against medical advice can cause bones to move and result in the need for surgery.
Courtrooms are asking for reliable scientific evidence in order to prevent wrongful convictions. Thus, a more rigorous approach to forensic science approved by scientific methods is promoted. The study of human blood dynamics in the context of forensic science is becoming a widespread research topic, although the physics behind wetting and drying of blood is not completely understood. Based on the morphological changes of drying blood pools, the following work presents a patentable method to quantitatively date these blood pools for forensic purposes. As for drying drops of blood, cracking patterns are observed but they are more disordered. Similar disordered crack patterns are observed in the case of gels, their evaporation process is, therefore, presented since this topic has been thoroughly investigated. We aim to find reliable patterns that could give information concerning the evolution of a blood pool over time to lead to practical application of this knowledge. An empirical model is established between final dried blood patterns and the generating mechanism, yielding application in bloodstain pattern analysis for forensic investigations.
These different stages are presented in the Fig. 2. These different steps of evaporation recall sol-gel processing with first the formation of a gel, evaporation from the surface followed by evaporation through the porous media. Finally cracking is observed as well. To understand the evaporation processes of blood, some analogy between a sol-gel transition and blood pools drying could, therefore, be envisaged.
One of the first observations concerning the sol-gel transition is that the process goes through different stages. First the sol transforms into a gel, which presents viscous and elastic properties. The clusters grown either by polymeric condensation or by particle aggregation assemble together to form a giant cluster called gel. Once the gel has formed, evaporation then takes place through this porous media. First the body of the system shrinks and the volume loss corresponds to the volume that has evaporated. After a critical point the body becomes rigid and stops shrinking. The liquid then recedes inside leaving near the surface air-filled pores. However evaporation continues to occur at the surface. Finally when only a small amount of liquid is left in some isolated pores, evaporation can only take place inside the system followed by vapour diffusion to the outside. Consequently drying of gels can be divided into several drying stages. Already in 1986 Dwivedi examined this process in some detail by studying the drying process of alumina gels of different thicknesses focusing on the mass loss over time. As a result he found that about 7% of the initial mass of gel is left after drying. In the case of blood pools, it was similarly shown that 23% of the initial mass is left after drying8. Dwivedi then looked at the different drying stages and found that alumina gels undergo three drying stages. The first stage is a constant rate period (CRP)19,20,21 where the volume decrease of the gel is equal to the volume of liquid lost by evaporation. In this stage, the evaporation rate appears to be comparable to that of an open dish of water22. A critical point is reached at the end of this stage, inducing the shrinkage to stop. Subsequently to this, cracking of the gel is more likely to occur. After the critical point, gels undergo a first falling rate (FRP1) where the liquid flows through partially empty pores, followed by a second falling rate (FRP2) corresponding to the final stage of drying. In this final stage, evaporation occurs inside the body and the liquid diffuses to the surface in the form of vapour. The description of the sol-gel transition and the drying of inorganic gels represent a classic work where the mechanisms are well established19. Therefore, examining its characteristics is interesting since we can envisage that the drying process of blood is likely to present some similarities, which will now be presented.
Blood is comparable to a colloidal solution where plasma corresponds to the aqueous phase since plasma is a water based solution, composed of 90 to 92% water, of 7 to 8% plasma proteins and the last 1 to 2% are trace amounts of other constituents23. Therefore a first simple study was made to follow the mass loss of the blood pools over time and to compare them to pools of water. Natural water evaporation is of course a well known phenomenon, but to our best knowledge actual research papers have focused mainly on natural evaporation from open water, ponds or water baths but no work has focused on the drying of a water pool formed by natural spreading. To compare water evaporation to blood evaporation, blood and water pools were created in parallel and dried in exactly the same conditions. Two different surfaces, linoleum and varnished oak wood, were tested in two different humidities of 20% and 30%. Since the pools had different drying durations, tf, and initial masses, mi, the obtained results were normalised as presented in Fig. 4 in order to compare both types of pools.
This constant value of the evaporation rate of water as a function of water left in blood implies that using the area analysis the dynamics can be predicted. Nonetheless the plateau appears to be different for the four pools. Several parameters must act. A simple relation describing the evaporation rate of a free surface based on convection already exists, given by29:
The various characteristics of a pool added to the variability of the surrounding parameters lead thus to a very complex problem. It appears that all these parameters are related together, as would suggest the results presented in Fig. 11. This last result presents a very interesting approximation suggesting that drying blood pools are very similar to gels. Although the pools were dried in similar conditions, mainly same humidity and same temperature, these parameters should be considered in further studies, as they are known to have an influence on evaporation. With temperature increase, diffusion coefficients are known to increase. This suggests that temperature can affect greatly the evaporation rates. Relative humidity affects evaporation as well since diffusion coefficients are known to decrease as the relative humidity increases. Further research should be devoted to seek out on how could temperature affect the plateau obtained for pools drying at 23 ± 1 °C. Fundamentally it can be accepted that the shape of a pool and the surroundings parameters are key to understand the evaporation rates. Undeniably the geometry affects the evaporation rate since some geometry would favour evaporation. For two pools of identical volume, the round pool will have its Knudsen layer saturated in vapour faster than the thin and stretched pool. The evaporation of the thin pool will be favoured, it will thus have a greater evaporation rate. Although estimating the geometry of a pool exhibits some uncertainty, the fact of taking the geometry in consideration already erases a large amount of errors. Moreover the obtained correlation can find very interesting practical application.
In this study the evaporation dynamics of blood have been described in detail and some similarities with the sol-gel transition were found. Indeed blood is similar to a colloidal suspension with RBCs being the dispersed phase, and plasma the aqueous phase. After coagulation and fibrin precipitation, blood forms a gel like system that will then dry following different evaporation rates. This evaporation rate has been compared to the evaporation rate of pools of water drying in similar conditions. Finally, some of the pool characteristics were assessed such as the size and the shape of the pool. A blood pool is an intermediate system between a drop and a larger stretch of liquid. The latter corresponds to a system involving one dimensional heat and mass transfers. For the blood pool the evaporation at the triple line influences the entire evaporation rate. As a result we found that the shape influences the rate, which is expressed in a shape factor. The size of a pool, of course interferes with evaporation since, the greater is the volume that has to evaporate. Moreover, the drying front of the pool evolves in a non-uniform manner since it can start evolving towards the centre on one side while on the other side the pool is still in a gel like phase. Ultimately, all these parameters are linked to the advancing drying front. We have investigated the evolution of the drying front and related it to the evaporation rate of water, J*. By using the wet area of the pool to calculate J*, an almost constant value of the evaporation rate was observed. Then by incorporating the different variables that act int the evaporation process of a pool, an approximative constant value of diffusion coefficient was observed for pools of various sizes and shapes, but drying in the same conditions. Using this approximation, it became possible to calculate the time at which a pool, dried in the same conditions, was formed. Nonetheless, this last correlation should be investigated further for more pools, of different shapes and larger sizes, and drying at different temperatures and humidities. Some effort on the research should be turned towards this issue as it could then bring a modelling of the evaporation of blood pools, which could then be monitored on a crime scene simply by following the drying front and using a reference table. This study used blood from healthy volunteers, males and females with haematocrit values ranging from 36.2 to 47.1%. Individual biological parameters did not show any significant influence on the evaporation dynamics. However other physiological parameters such illnesses, like haemophilia, or the intake of drugs, like aspirin, could have an indirect influence on evaporation since they are known to interfere with clotting. Future work on individual physiological aspects would thus improve the proposed model. Nonetheless, this investigation has demonstrated pioneering results concerning the drying of blood pools from healthy subjects, which may find exploitation in forensic analysis. 2b1af7f3a8