Category Archives: Science

Legal, Science, Scotland, Society, Technology

Forensic Science: Scientists will bring an end to unsolved crime

FORENSICS

SCOTLAND’S top forensics scientist has predicted it will be virtually impossible to get away with a crime within a generation due to advances in DNA technology.

The director of forensic services at the Scottish Police Authority (SPA), Tom Nelson, said rapid improvements made it more likely that criminals would always be found out.

. Related DNA Phenotyping…

He said the SPA was looking at ’12 cold cases’ in which modern techniques were being used to analyse old evidence in an effort to bring offenders to justice.

New methods mean DNA traces can be found on clothing and other materials even when there is no blood – something that would have been impossible in the past.

Mr Nelson said one of the guiding principles of forensic science is ‘every contact leaves a trace’.

He said: ‘We may be recovering material at the moment which doesn’t necessarily allow us to detect an individual but, as science develops in the next 15 years, that will become possible – science is always moving on.’

Mr Nelson said the challenge for police forensics experts was to ‘throw everything that we have in our toolbox’ at securing genetic samples from crime scenes.

He said that thanks to improvements in DNA analysis ‘an individual may commit a crime and think they have got away with it for a number of years, but I believe that individual will be detected’.

The SPA’s current caseload features 12 cold cases, stretching back up to 20 years, in which forensic investigators are analysing evidence to gauge whether new breakthroughs are possible.

Mr Nelson pointed to forensics work which contributed to the conviction of nine members of a gang who were jailed for a total of 87 years in January for drug and gun offences.

Their crimes included the ‘merciless’ torture of a man over a cocaine debt and an arsenal of weapons hidden in a car. A report by Mr Nelson revealed that more than 200 DNA samples were recovered from seized firearms. More than 1,000 DNA samples and 1,000 fingerprints were recovered from various scenes.

The results of these tests identified all of the initial suspects in the case and uncovered an additional six people that were not initially linked to the group until the forensic results were provided.

Mr Nelson’s report states: ‘Criminals should be aware that they cannot escape without leaving traces of material at the scene of their crime.’

Modern forensic techniques include DNA 24, a profile kit which targets 24 parts of a person’s DNA, whereas in the past it was only possible to look at 11 areas.

However, the daughter of a former police officer, who was wrongly accused of perjury when a fingerprint found at a murder scene in 1997 was mistakenly identified as hers, questioned the SPA’s confidence in forensic science.

He said: ‘While forensics has come a long way, they still perpetuate this fiction of perfection which is not true – rubbish in, rubbish out. Human error in the collection of forensic evidence and in its analysis is still a contributor to miscarriages of justice.’

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Arts, History, Philosophy, Science

Philosophy: The four elements and atomism

GREEK PHILOSOPHY

The dawn of scientific thought in Ancient Greece.

THE question of what the universe is made of was still a major concern of Greek philosophers in the fifth century BCE. A native of Akragas in Sicily named Empedocles thought that everything was composed of a single element (known as the Milesian line of thought). Later, however, he took this a step further, identifying four distinct elements – earth, water, air and fire – which in different proportions formed all the different substances in the universe. Developing his ideas from the monism of Parmenides, he argued that these elements must therefore be eternal and unalterable, but reasoned that change was possible if some sort of force altered the mixture of elements.

He suggested that two opposing forces, which he poetically called ‘Love’ and ‘Strife’, caused attraction or separation of the elements and brought about changes in the composition of substances. His classification of the substances later known as the four classical elements was widely accepted by philosophers and was a cornerstone of alchemy until the Renaissance (the transition from the Middle Ages to the Modern Era and covering the span between the 14th and 17th centuries).

Democritus and Leucippus: atomism

A theory of matter proposed by Leucippus and his pupil Democritus was less influential at the time than the ‘four elements’ proposed by their contemporary Empedocles. In retrospect, it seems closer to modern scientific understanding. They suggested that everything in the universe is composed of minute, unalterable and indivisible particles, which they called atoms (from the Greek atomos, uncuttable). These, they argued, are free to move through empty space, combining in constantly changing configurations.

The assertion there is such a thing as a void, an empty space, may be one reason these ideas were originally considered unacceptable. According to their theory, the number of atoms is infinite, and different kinds of atoms with different characteristics determine the properties of the substance they form together. Because the atoms are indestructible, when a substance, or even a human body decays, its atoms are dispersed and reconstituted in another form.

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Science

Questions of Science: Free the atoms

Oxygen has a slightly greater density than nitrogen. Why, then, don’t these main constituents of air separate out?

MD overlapGAS MOLECULES move rapidly at room temperature, with oxygen and nitrogen travelling at around 500 metres per second, so they obviously collide frequently. This allows the oxygen and nitrogen molecules to mingle and mix, rather like large numbers of people on a nightclub dance floor, in a process known as diffusion. Convection, the transfer of heat within the atmosphere, also plays an important role in this gas mixing process.

Gas mixing is a spontaneous process. This means that if you had a container with two compartments separated by a barrier, with one compartment containing pure nitrogen and the other pure oxygen, the two gases would automatically mix or diffuse as soon as the barrier was removed.

A change in the ratio of oxygen to nitrogen would be expected in a hypothetical quiescent atmosphere. However, constant mixing occurs in the real atmosphere, driven by the Earth’s rotation and by differences in density between hot air at the Earth’s surface and colder air higher up.

Up to altitudes of between 80 and 120 kilometres this mixing results in a uniform concentration of oxygen and nitrogen – which respectively make up approximately 21 per cent and 78 per cent of the atmosphere.

This region is known as the homosphere. Partial stratification of the two gases does occur above 120 kilometres, in the heterosphere, where the density of air is much lower than at the surface and the efficiency of bulk mixing processes is reduced.

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If there were no circulation in the atmosphere, the oxygen would tend to concentrate in the lower strata. This process would take millions of years once circulation ceased because molecules of oxygen (and, indeed, nitrogen) are constantly colliding with other molecules. This means it would take a long time for a particular molecule to fall from its starting point to the ground. Once it hit the ground, it would bounce and eventually rise again to a great height, only to fall again. This would be repeated frequently if no other variable, such as temperature, changed.

Although the individual molecules continue to travel up and down, each ‘species’ of oxygen and nitrogen would eventually reach an equilibrium distribution of molecules per unit volume as a function of height. This species density will decrease with height by an amount that depends on the molecular weight of the species. So, the oxygen would fall off with height slightly faster than the nitrogen. At high altitudes, the air would become richer in nitrogen, but then other gases such as water vapour, neon, methane, helium and hydrogen would dominate.

In fact, atmospheric circulation and turbulence prevents this from happening in the lower atmosphere. But in the very high atmosphere there is not much circulation and the composition does become dominated by atomic oxygen. Above 600 kilometres this is superseded by helium, and eventually by atomic hydrogen.

science in motion

Science-in-motion: a series of short articles following topics in science.

. Molecular geometry

This describes the overall shape of a molecule in terms of how the atoms inside it are arranged. Examples of simple structures are linear molecules like carbon dioxide (O=C=O) and tetrahedral molecules like methane, which consists of a carbon atom with four hydrogen atoms surrounding it at the corners of a tetrahedron.

Trigonal-bipyramidal molecules are shaped like two pyramids back to back, while octahedral molecules have a shape like an eight-sided solid. Octahedral molecules include the compound sulphur hexafluoride (SF6).

‘Isomers’ are compounds that have the same chemical formula but different molecular structures. For instance, the sugar fructose is an isomer of glucose – they have the same formula C6H12O6, but their atoms are arranged in different ways. Sometimes, two isomers are mirror images of each other, in which case the molecule is said to be ‘chiral’ and the two mirror-image forms are called enantiomers. Chiral molecules include most amino acids (which are the building blocks of proteins).

Molecular Geometry

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