Paper Example on Blood Sampling in Forensic Analysis: Desiccated Blood Samples

Introduction

The collection of blood samples is very significant in forensic analysis. Diffrerent ways of blood sampling have been applied, which includes desiccated blood samples (Chao et al. 2016). This methond is executed by dissemination of blood drop capping a permeable substrate called DBS card, during a instantaneous diffusion, and distribution within fractions of the permeable substrate. The understanding of the exchanges between blood and authentic face is an intricate issue because of fluid mechanical behavior (Smith and Brutin, 2018). Therefore, blood is a non-Newtonian fluid which display complex nature which is dependent on the immediate setting and its biological properties.

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Imbibition Dynamics

Using a directional angle analysis experiment where the bloodtstains on woven fabric were conducted to quantify uncertainity on impacts that directional angles have, it was established that the stains formed on fabric properties are affected by imbibition dynamics (Agrawal, Barnet, and Attinger, 2017). The resistance of viscous forces and wetting forces causes various aspects of imbibition dynamics such as capillary transportation of liquid. In reurn, h imbbibiion dynamics leads o several deformaions as well as ampificaion of he bloodstains. Due to the effects of such factors, measurement errors arose during the experiment. As stipulated by Laan et al. (2015), the spreading behaviour exhibited by the bloodstains, arises as a result of interpolation between capillary regime and viscous regime as shown in the following equation;

Wmax/Do= Re1/5 p1/2sina(A+P12sina45) P stands for impact number given by P= WeRe- 25 and A = 1.24

The calculation of width neccesitates the numerical solution of the volume of bloodstains and impact angle for the impact velocity. Besides, I neccesitates the determination of motion of a projected droplet flying through the air as influenced by the drag and gravity (Laan et al., 2015). The extent to which a blood droplet spreads is determined by the volume, where the bigger the size of droplet the bigger the stains.

Mostly the distribution research is done to examine the length of the spreading path,time taken for by the blood drop to reach certain heights, the angle of contact between the blood and the substrate and the length of half the wetted spot. The distribution and the wetting of the substrate is a difficult process that is determined by both chemical and physical nature. Study has been done on the conduct of the wetting and the distribution of Newtonian and non-newtonian fluids. Nonetheless, for the permeable substrate, very few studies have been done, hence little is known. Smith and Brutin (2018) argued that contact between the blood, the surface of the permeable material and foreign materials is a recent notion that has not received stern examination in spite of blood being a key area in offence analysis. The interactions between the blood and the surface of the permeable substrate is complicated since the blood is a complex fluid which is different from other common fluid that have been studied (Smith and Brutin, 2018).

Chao et al. (2016) explored the distribution/imbibition of Newtonian fluids on a permeable film to comprehend how the hydrophobicity affets the substrate. According to the rport done by Chao et al. (2015), the blood possess traits of a non-Newtonian liquid such as the shinning behavior. Hence, the natural philosophy of blood can be considered using different developed philosophical model. One such model is the rheometer that is used together with plan geometry. As Chao et al. (2015) noted, the distribution/imbibition of Newtonian fluids used in bloodstain examination is of two main phases. In the fiisrt stage the radius of the established by increases as the duct spreads (Arany and Ohtani, 2011). The spreading out of the radius takes place quicker in contrast to the contraction, this is so since the filter paper is being inhibited. The increase in radius occurs untill a compensate between the spreading out and contraction is achieved, and the utmost radius is attained. Once the balance is achieved and the utmost radius achieved, the start of the next phase begins with a contraction and h faction of the area begins to swell.

Drying Dynamics

In their study, Laan et al. (2016) found that the drying process of blood proceeds in five steps which include, coagulation, gelation, rim dessicacion, centre dessication and final dessication. The wetting area kept on to swelling up to when the droplet vanished completely. Throughout the research, the silhouette of the droplets had no alteration but sustained their sphere-shaped cap all through the whole distribution period. This was a good sign of the accord between the process and the theoretical postulation. Moreover, the rotund form necessitated the computation of the dynamic angle. Each time blood the substrate interacts, two major boundary movements take place, that is the wetting and evaporation. The ability of the blood to wet is accountable for the stability experienced on applied forces. On the other hand evaporation accounts forthe h phase modification thattakes place throughout the contact (Smith and Brutin, 2018). Both wetting and evaporation are affected by environmental factors such as dampness, amount, wettability, hotness, the coarseness of the surface, Blood's clotting reaction and duration taken. When the blood exposed, outside the human being body, its characteristics changes. First of all the platelet is triggered, and this activates the coagulation cascade response. Smith and Brutin (2018) noted that wetting of blood has an effects on the the form it attains after being placed on the substrate. In addition, the means of by which different fluids wet substrate depict resemblance.

The evaporation of blood has been quantified using the evaporation mass flux, and has been found to contrast that of water. According to Smith and Brutin(2018), the evaporation of blood can be compared to the evaporation mechanism of pure fluids that have of connatural mass with a colloid concentrations. According to Bou Zeid and Brutin (2013), Bou Zeid and Brutin (2014) Bremmer et al. (2011) and Laan et al (2016), humidity above 60% alters the drying times of blood. The partens which are formed when the blood contacts the surface is dependent on the health of the individual. In this regard, the blood of a individual afflicted with hyperlipidemia displays different outline compared to a individual without such ailment (Smith and Brutin, 2018).

Theories Governing BPA

Impact Theory

According to this theory, when a blood drop strikes a dry solid surface from a particular height, energy some energy is lost due to velocity(de Goede et al., 2017). The velocity of the blood drop is then correlated to the pattern that the blood forms. Therefore, the pattern which is formed depends on the speed with which the blood drop falls off a particular height. Upon falling, the blood remains on the surface as it starts to dry and evaporate. The process of drying and evaporation is determined by various factors such as the adjacent properties, the surface on where the blood drop falls and the nature of the drop. Chao et al. (2015), stated that a coarse surface has effets on the ability of the blood to wet the substrate and how the blood spreads. When the irregularity of the surface increases, the blood drop alteration increases. Therefore, if the blood drop stains have equal volume, their alteration increases with the increase in roughness of the surface as shown below:

Splashing Phenomenon

The splash velocity refers to "the critical value of the impact velocity of the droplet beyond which splashing occurs" (de Goede et al., 2017, p. 5163). In a splashing phenomenon, a blood droplet can split up into minor droplets or stretch over a surface. When the velocity at which the droplets is high the impact on the surface is grater hence the falling droplets that splits up into smaller droplets. On the other hand if the velocity of the droplet is low the impact on the surface is less, hevce the droplet spreada over the surface. The atmospheric conditions have effects on the splashing velocity making splashing velocity a very vital parameter. According to de Goede et al. (2017), splashing happens once a tiny liquid layer disentigrates due to lift force created by the nearby air.

Background theory

After bleeding takes place, blood coagulate then dries leaving a pool of blood. As the blood dries up, the pool loses water through evaporation forming a solid state of matter comprising of red blood cells. Although the pools are found in the order of mililitres to litres, sampling at the crime scene focuses on the former. Upon deposition at the ground, the blood droplet spreads on the surface covering up an area. During the laying process, the surface tension acts on the tripple-line and its spread is can be established using the formula S = (cos o - 1) where S is the spreading parameter, denotes surface tension, and o, contact angle. Based on that formula, a contact angle greater than 90o, implies that the liquid cannot spread easily hence said to be non-wetting. The picture below shows a pool of blood;

Informed Discussion

When the blood is released for any body into the environment, it is spread in the air. This blood may fall on any surface (Arany and Ohtani, 2011). The shape of the blood drops depends on the surface where the droplet falls, falling speed, distance from the body to the surface and the angle with which the droplet falls on. Some of the most common shapes of the droplets includes, spherical, cryptic with extensions. The are three classes of bloodstains based on factors such as velocity of the bloodstain, impact angle, the distance, and blood volume. These classies of blood paens include: altered stains, spattered stains and passive stains among other smaller classifications.

Smaller blood droplets also tend to break away from the main droplet(Smith and Brutin, 2018). The measurements of the length and the width of the droplet are significant in computing for the angle of the contact. The angle of contact is important in establishing the events that occurred in the crime zone.

Modification of the angle of contact results to alteration of the formation of the droplet. If the droplet falls perpendicularly on an even surface, the resulting strain is spherical. The strain also shows extensions that are well spread out. If the angle of contact is less than 750 the extensions are quite pronounced in the course of the spatter (Agrawal, Barnet, and Attinger, 2017). The extensions increases as the angle of contact reduces, that is the extensions turn bigger converse the angle of contact. At a smaller acute angles the droplets splits to form other smaller derivative extensions with the shape of an 'exclamation mark' as shown figure below:

Void patterns

These are also important indicators; to point out that individual or item is missing in the felony sight. It is also an indicator that may be the body was moved to another area. The void patterns are key in establishing the location of the victim and the oppressor on the crime scene.

Critical Analysis of Literature

The analysis of blood strain is a forensic science that is concerned with information concerning how the blood strain comes once the blood is released. Most instances where...