Leonardo Da Vinci Perpetual Machine Assignment Example | Topics and Well Written Essays - 250 words

Leonardo Da Vinci Perpetual Machine - Assignment Example The model presented in the picture is probably the simplest among them, but it is definitely as good as others are. The main purpose of such layout was to create asymmetry using additional physical effects. This hypothetical perpetual wheel would revolve around its axis, and the metal pellets placed in the sections of the wheel would roll over, creating unevenness in load distribution and making the wheel keep on moving. However, eventually, Da Vinci admitted that the construction of a working perpetual machine is impossible. Commenting this conclusion, Da Vinci wrote that, interpreted into modern language, when the pellet (i.e. the weight) placed in one of the sections â€Å"moves farther from the pivot, the gravitational torque on it increases, but also the moment of inertia of the wheel is increased at the same time, which makes the gravitational torque less effective in increasing or sustaining motion of the wheel† (Simanek). In other words, the obtain effect is eventually zero. Moreover, Da Vinci concluded that every mechanical system inevitably loses its power through friction (Capra). Later, and especially at the dawn of the 20 century (intensive industrialization), the inventors tried to improve older prototypes of perpetual machines, but these attempts proved to be failure due to laws of physics (e.g. the principle of perpetual motion virtually violates two first laws of thermodynamics (Roy). In the end, the idea of a mechanism producing free energy without any outside sources or fuel was condemned as

Gene therapy Essay Example | Topics and Well Written Essays - 1250 words

Gene therapy - Essay Example Currently, research is going on for gene therapy by various approaches in different parts of the world for various diseases like combined immuno-deficiencies, hemophilia, Parkinson's disease, cancer and even HIV (Verma and Weitzman, 2005). Though gene therapy has been under research for the past 2 decades, no single gene therapy has been approve for clinical use. The main reason for this is safety concerns pertaining to gene therapy trials and treatment. In this essay, various strategies to increase the safety of gene therapy will be discussed through review of suitable literature. Safety issues related to gene therapy are mainly related to the methods employed in gene therapy. There are basically 2 methods of gene therapy and they are ex-vivo therapy and in-vivo therapy. In ex-vivo therapy, gene delivery is done in cells after being removed from the body (Hecht, 2004). The cells used thus are basically grown in the laboratory. The cells are than modified outside the body and then tr ansplanted back into the body. In some research trials, cells from blood or born marrow are taken out and cultured in a laboratory. Thereafter, the cells are exposed to the virus with the desired gene. The virus infects the cells and transfers the therapeutic genetic material into the nucleus of the cells. After this, the cells are injected into the patient’s body by vein. In in vivo therapy, gene delivery is done in the cells that are still in the body. The simplest method of introducing therapeutic genetic material into the cells is direct introduction into target cells. However, this method is not practical because it can be used only with certain tissues and requires large amounts of DNA. Other methods are there wherein the genes are delivered into cells by vectors like viruses or bacteria, by electroporation or tiny synthetic "envelopes" of fat molecules (Hecht, 2004). Of these, the most commonly used vector is virus. Vector is the carrier of the gene. Viruses are used a s vectors to deliver genetic material to the nucleus of the cell that contains its DNA. The natural ability of a virus to enter a cell is used for this purpose. The viruses used for gene therapy are retrovirus, adenovirus, adeno-associated virus and herpes simplex virus (Genetics Home Reference, 2008). While preparing the vectors for gene therapy, the DNA coding for a part or whole of the normal genes of the virus to be used as a carrier is removed and replaced with the treatment gene. The carriers are engineered in such a way that there ability to enter the cells is not lost but they cannot reproduce. Genes delivered by tiny synthetic "envelopes" of fat molecules enter the cell by cell membrane which has very high concentration of fat molecules. In electroporation, the genes are delivered into the cells by creating tiny openings in the cell membrane. This is done by using a bionic chip. The chip contains a single living cell embedded in a tiny silicon circuit (Hecht, 2004). Another method of gene therapy is where the therapeutic gene gets inside the target cell by chemically linking the DNA to a molecule that will bind to special cell receptors. After binding to these receptors, the DNA is engulfed by the cell membrane and passed into the interior of the target cell. However, this is less effective than the other methods (Genetics Home R