Erysipelothrix is a genus of bacteria containing four described species, Erysipelothrix rhusiopathiae, Erysipelothrix tonsillarum, Erysipelothrix inopinata and Erysipelothrix larvae. Additional species have been proposed based on DNA-DNA hybridization studies "The hallmark of Erysipelothrix is the presence of a type B cell wall, in which the peptide bridge is formed between amino acids at positions 2 and 4 of adjacent peptide side-chains and not, as in the vast majority of bacteria, between amino acids at positions 3 and 4."The best known species within the genus is Erysipelothrix rhusiopathiae, the cause of erysipelas of domestic pigs and other animal species. In humans, E. rhusiopathiae infections are termed erysipeloid. Erysipelothrix tonsillarum has been described as a pathogen for dogs and has been isolated from the tonsils of healthy pigs and cattle. Disease caused by E. inopinata or E. larvae have not been described. Bacteria of genus Erysipelothrix are straight, or curved, nonmotile rods which may exist singly, in V-shaped pairs, or in short chains.
Some strains have a tendency to form long filaments. The bacteria are Gram-positive but can be mistaken for Gram-negative bacteria during analysis because they lose their staining easily, they are aerobic to facultatively anaerobic but not acid-fast. Erysipelothrix at BacDive - the Bacterial Diversity Metadatabase Erysipelothrix at MicrobeWiki
Staphylococcus is a genus of Gram-positive bacteria in the family Staphylococcaceae in the order Bacillales. Under the microscope, they appear spherical, form in grape-like clusters. Staphylococcus species are facultative anaerobic organisms; the name was coined in 1882 by Scottish surgeon and bacteriologist Alexander Ogston, following the pattern established five years earlier with the naming of Streptococcus. It combines the prefix "staphylo-", suffixed by the Modern Latin: coccus, lit.'spherical bacterium'. Staphylococcus includes at least 40 species. Of these, nine have two subspecies, one has three subspecies, one has four subspecies. Most are harmless and reside on the skin and mucous membranes of humans and other organisms. Staphylococcus has been found to be a nectar-inhabiting microbe. Found worldwide, they are a small component of soil microbial flora; the taxonomy is based on 16s rRNA sequences, most of the staphylococcal species fall into 11 clusters: S. aureus group – S. argenteus, S. aureus, S. schweitzeri, S. simiae S. auricularis group – S. auricularis S. carnosus group – S. carnosus, S. condimenti, S. massiliensis, S. piscifermentans, S. simulans S. epidermidis group – S. capitis, S. caprae, S. epidermidis, S. saccharolyticus S. haemolyticus group – S. devriesei, S. haemolyticus, S. hominis S. hyicus-intermedius group – S. agnetis, S. chromogenes, S. cornubiensis, S. felis, S. delphini, S. hyicus, S. intermedius, S. lutrae, S. microti, S. muscae, S. pseudintermedius, S. rostri, S. schleiferi S. lugdunensis group – S. lugdunensis S. saprophyticus group – S. arlettae, S. caeli, S. cohnii, S. equorum, S. gallinarum, S. kloosii, S. leei, S. nepalensis, S. saprophyticus, S. succinus, S. xylosus S. sciuri group – S. fleurettii, S. lentus, S. sciuri, S. stepanovicii, S. vitulinus S. simulans group – S. simulans S. warneri group – S. pasteuri, S. warneriA 12th group – that of S. caseolyticus – has now been removed to a new genus, the species of which are the closest known relatives of Staphylococcus.
Two species were described in 2015 - Staphylococcus argenteus and Staphylococcus schweitzeri - both of which were considered variants of S. aureus. A new coagulase negative species - Staphylococcus edaphicus - has been isolated from Antarctica; this species is a member of the S. saprophyticus group. S. aureus subsp. AureusS. Aureus subsp. Anaerobius S. capitis subsp. CapitisS. Capitis subsp. Urealyticus S. carnosus subsp. CarnosusS. Carnosus subsp. Utilis S. cohnii subsp. CohniiS. Cohnii subsp. Urealyticus S. equorum subsp. EquorumS. Equorum subsp. Linens S. hominis subsp. HominisS. Hominis subsp. Novobiosepticus S petrasii subsp. CroceilyticusS petrasii subsp. JettensisS petrasii subsp. PetrasiiS petrasii subsp. Pragensis S. saprophyticus subsp. BovisS. Saprophyticus subsp. Saprophyticus S. schleiferi subsp. CoagulansS. Schleiferi subsp. Schleiferi S. sciuri subsp. CarnaticusS. Sciuri subsp. RodentiumS. Sciuri subsp. Sciuri S. succinus subsp. CaseiS. Succinus subsp. Succinus Based on an analysis of orthologous gene content three groups have been proposed.
Group A includes S. aureus, S. capitis, S. epidermidis, S. haemolyticus, S. hominis, S. lugdunensis, S. pettenkoferi, S. simiae and S. warneri. Group B includes S. cohnii, S. equorum, S. saprophyticus and S. xylosus. Group C includes S. intermedius and S. pseudintermedius. The S. saprophyticus and S. sciuri groups are novobiocin-resistant, as is S. hominis subsp. Novobiosepticus. Members of the S. sciuri group are oxidase-positive due to their possession of the enzyme cytochrome c oxidase. This group is the only clade within the staphylococci to possess this gene; the S. sciuri group appears to be the closest relations to the genus Macrococcus. S. pulvereri has been shown to be a junior synonym of S. vitulinus. Within these clades, the S. haemolyticus and S. simulans groups appear to be related, as do the S. aureus and S. epidermidis groups. S. Lugdunensis appears to be related to the S. haemolyticus group. S. petrasii may be related to S. haemolyticus. The taxonomic position of S. lyticans, S. pettenkoferi, S. petrasii, S. pseudolugdunensis has yet to be clarified.
The published descriptions of these species do not appear to have been validly published. Assignment of a strain to the genus Staphylococcus requires it to be a Gram-positive coccus that forms clusters, has an appropriate cell wall structure and G + C content of DNA in a range of 30–40 mol%. Staphylococcus species can be differentiated from other aerobic and facultative anaerobic, Gram-positive cocci by several simple tests. Staphylococcus species are facultative anaerobes. All species grow in the presence of bile salts. All species of Staphylococcus aureus were once thought to be coagulase-positive, but this has since been disproven. Growth can occur in a 6.5% NaCl solution. On Baird Parker medium, Staphylococcus species grow fermentatively, except for S. saprophyticus, which grows oxidatively. Staphylococcus species are susceptible to furazolidone. Further biochemical testing is needed to identify to the species level; when these bacteria divide, they do so along two axes. This is as opposed to streptococci.
One of the most important phenot
The vertebral column known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord found in all chordates has been replaced by a segmented series of bone: vertebrae separated by intervertebral discs; the vertebral column houses a cavity that encloses and protects the spinal cord. There are about 50,000 species of animals; the human vertebral column is one of the most-studied examples. In a human's vertebral column there are thirty-three vertebrae; the articulating vertebrae are named according to their region of the spine. There are twelve thoracic vertebrae and five lumbar vertebrae; the number of vertebrae in a region overall the number remains the same. The number of those in the cervical region however is only changed. There are ligaments extending the length of the column at the front and the back, in between the vertebrae joining the spinous processes, the transverse processes and the vertebral laminae.
The vertebrae in the human vertebral column are divided into different regions, which correspond to the curves of the spinal column. The articulating vertebrae are named according to their region of the spine. Vertebrae in these regions are alike, with minor variation; these regions are called the cervical spine, thoracic spine, lumbar spine and coccyx. There are twelve thoracic vertebrae and five lumbar vertebrae; the number of vertebrae in a region overall the number remains the same. The number of those in the cervical region however is only changed; the vertebrae of the cervical and lumbar spines are independent bones, quite similar. The vertebrae of the sacrum and coccyx are fused and unable to move independently. Two special vertebrae are the axis, on which the head rests. A typical vertebra consists of two parts: the vertebral arch; the vertebral arch is posterior. Together, these enclose the vertebral foramen; because the spinal cord ends in the lumbar spine, the sacrum and coccyx are fused, they do not contain a central foramen.
The vertebral arch is formed by a pair of pedicles and a pair of laminae, supports seven processes, four articular, two transverse, one spinous, the latter being known as the neural spine. Two transverse processes and one spinous process are posterior to the vertebral body; the spinous process comes out the back, one transverse process comes out the left, one on the right. The spinous processes of the cervical and lumbar regions can be felt through the skin. Above and below each vertebra are joints called facet joints; these restrict the range of movement possible, are joined by a thin portion of the neural arch called the pars interarticularis. In between each pair of vertebrae are two small holes called intervertebral foramina; the spinal nerves leave the spinal cord through these holes. Individual vertebrae are named according to their position. From top to bottom, the vertebrae are: Cervical spine: 7 vertebrae Thoracic spine: 12 vertebrae Lumbar spine: 5 vertebrae Sacrum: 5 vertebrae Coccyx: 4 vertebrae The upper cervical spine has a curve, convex forward, that begins at the axis at the apex of the odontoid process or dens, ends at the middle of the second thoracic vertebra.
This inward curve is known as a lordotic curve. The thoracic curve, concave forward, begins at the middle of the second and ends at the middle of the twelfth thoracic vertebra, its most prominent point behind corresponds to the spinous process of the seventh thoracic vertebra. This curve is known as a kyphotic curve; the lumbar curve is more marked in the female than in the male. It is convex anteriorly, the convexity of the lower three vertebrae being much greater than that of the upper two; this curve is described as a lordotic curve. The sacral curve begins at the sacrovertebral articulation, ends at the point of the coccyx; the thoracic and sacral kyphotic curves are termed primary curves, because they are present in the fetus. The cervical and lumbar curves are compensatory or secondary, are developed after birth; the cervical curve forms when the infant is able to sit upright. The lumbar curve forms from twelve to eighteen months, when the child begins to walk. Anterior surfaceWhen viewed from in front, the width of the bodies of the vertebrae is seen to increase from the second cervical to the first thoracic.
From this point there is a rapid diminution, to the apex of the coccyx. Posterior surfaceFrom behind, the vertebral column presents in the median line the spinous processes. In the cervical region these are short and bifid. In the upper part of the thoracic region they are directed obliquely downward.
Salmonella is a genus of rod-shaped Gram-negative bacteria of the family Enterobacteriaceae. The two species of Salmonella are Salmonella Salmonella bongori. S. enterica is the type species and is further divided into six subspecies that include over 2,600 serotypes. Salmonella species are non-spore-forming, predominantly motile enterobacteria with cell diameters between about 0.7 and 1.5 µm, lengths from 2 to 5 µm, peritrichous flagella. They are chemotrophs, obtaining their energy from oxidation and reduction reactions using organic sources, they are facultative aerobes, capable of generating ATP with oxygen when it is available, or when oxygen is not available, using other electron acceptors or fermentation. S. enterica subspecies are found worldwide in the environment. S. bongori is restricted to cold-blooded animals reptiles. Salmonella species are intracellular pathogens. Nontyphoidal serotypes can be transferred from human-to-human, they invade only the gastrointestinal tract and cause salmonellosis, the symptoms of which can be resolved without antibiotics.
However, in sub-Saharan Africa, nontyphoidal Salmonella can be invasive and cause paratyphoid fever, which requires immediate treatment with antibiotics. Typhoidal serotypes can only be transferred from human-to-human, can cause food-borne infection, typhoid fever, paratyphoid fever. Typhoid fever is caused by Salmonella invading the bloodstream, or in addition spreads throughout the body, invades organs, secretes endotoxins; this can lead to life-threatening hypovolemic shock and septic shock, requires intensive care including antibiotics. The collapse of the Aztec society in Mesoamerica is linked to a catastrophic Salmonella outbreak, one of humanity's deadliest, that occurred after the Spanish conquest; the genus Salmonella is part of the family of Enterobacteriaceae. Its taxonomy has the potential to confuse; the genus comprises two species, S. bongori and S. enterica, the latter of, divided into six subspecies: S. e. enterica, S. e. salamae, S. e. arizonae, S. e. diarizonae, S. e. houtenae, S. e. indica.
The taxonomic group contains more than 2500 serotypes defined on the basis of the somatic O and flagellar H antigens. The full name of a serotype is given for example, Salmonella enterica subsp.. Enterica can be abbreviated to Salmonella Typhimurium. Further differentiation of strains to assist clinical and epidemiological investigation may be achieved by antibiotic sensitivity testing and by other molecular biology techniques such as pulsed-field gel electrophoresis, multilocus sequence typing, whole genome sequencing. Salmonellae have been clinically categorized as invasive or noninvasive based on host preference and disease manifestations in humans. Salmonella was first visualized in 1880 by Karl Eberth in the Peyer's patches and spleens of typhoid patients. Four years Georg Theodor Gaffky was able to grow the pathogen in pure culture. A year after that, medical research scientist Theobald Smith discovered what would be known as Salmonella enterica. At the time, Smith was working as a research laboratory assistant in the Veterinary Division of the United States Department of Agriculture.
The department was under the administration of a veterinary pathologist. Salmonella Choleraesuis was thought to be the causative agent of hog cholera, so Salmon and Smith named it "Hog-cholerabacillus"; the name Salmonella was not used until 1900, when Joseph Leon Lignières proposed that the pathogen discovered by Salmon's group be called Salmonella in his honor. Most subspecies of Salmonella produce hydrogen sulfide, which can be detected by growing them on media containing ferrous sulfate, such as is used in the triple sugar iron test. Most isolates exist in two phases, a motile phase I and a nonmotile phase II. Cultures that are nonmotile upon primary culture may be switched to the motile phase using a Craigie tube or ditch plate. RVS broth can be used to enrich for Salmonella species for detection in a clinical sample. Salmonella can be detected and subtyped using multiplex or real-time polymerase chain reactions from extracted Salmonella DNA. Mathematical models of Salmonella growth kinetics have been developed for chicken, pork and melons.
Salmonella reproduce asexually with a cell division interval of 40 minutes. Salmonella species lead predominantly host-associated lifestyles, but the bacteria were found to be able to persist in a bathroom setting for weeks following contamination, are isolated from water sources, which act as bacterial reservoirs and may help to facilitate transmission between hosts. Salmonella is notorious for its ability to survive desiccation and can persist for years in dry environments and foods; the bacteria are not destroyed by freezing. They perish after being heated to 60 °C for 12 min. To protect against Salmonella infection, heating food for at least 10 minutes to an internal temperature of 75 °C is recommended. Salmonella species can be found in the digestive tracts of humans and animals reptiles. Salmonella on the skin of reptiles or amphibians can be passed to people. Food and water can be contaminated with the bacteria if they come in contact with the feces of infected people
A joint or articulation is the connection made between bones in the body which link the skeletal system into a functional whole. They are constructed to allow for different types of movement; some joints, such as the knee and shoulder, are self-lubricating frictionless, are able to withstand compression and maintain heavy loads while still executing smooth and precise movements. Other joints such as sutures between the bones of the skull permit little movement in order to protect the brain and the sense organs; the connection between a tooth and the jawbone is called a joint, is described as a fibrous joint known as a gomphosis. Joints are classified both functionally. Joints are classified structurally and functionally. Structural classification is determined by how the bones connect to each other, while functional classification is determined by the degree of movement between the articulating bones. In practice, there is significant overlap between the two types of classifications. Monoarticular – concerning one joint oligoarticular or pauciarticular – concerning 2–4 joints polyarticular – concerning 5 or more joints Structural classification names and divides joints according to the type of binding tissue that connects the bones to each other.
There are four structural classifications of joints: fibrous joint – joined by dense regular connective tissue, rich in collagen fibers cartilaginous joint – joined by cartilage. There are two types: primary cartilaginous joints composed of hyaline cartilage, secondary cartilaginous joints composed of hyaline cartilage covering the articular surfaces of the involved bones with fibrocartilage connecting them. Synovial joint – not directly joined – the bones have a synovial cavity and are united by the dense irregular connective tissue that forms the articular capsule, associated with accessory ligaments. Facet joint – joint between two articular processes between two vertebrae. Joints can be classified functionally according to the type and degree of movement they allow: Joint movements are described with reference to the basic anatomical planes. Synarthrosis – permits little or no mobility. Most synarthrosis joints are fibrous joints. Amphiarthrosis – permits slight mobility. Most amphiarthrosis joints are cartilaginous joints.
Synovial joint – movable. Synovial joints can in turn be classified into six groups according to the type of movement they allow: plane joint and socket joint, hinge joint, pivot joint, condyloid joint and saddle joint. Joints can be classified, according to the number of axes of movement they allow, into nonaxial, monoaxial and multiaxial. Another classification is according to the degrees of freedom allowed, distinguished between joints with one, two or three degrees of freedom. A further classification is according to the number and shapes of the articular surfaces: flat and convex surfaces. Types of articular surfaces include trochlear surfaces. Joints can be classified based on their anatomy or on their biomechanical properties. According to the anatomic classification, joints are subdivided into simple and compound, depending on the number of bones involved, into complex and combination joints: Simple joint: two articulation surfaces Compound joint: three or more articulation surfaces Complex joint: two or more articulation surfaces and an articular disc or meniscus The joints may be classified anatomically into the following groups: Joints of hand Elbow joints Wrist joints Axillary articulations Sternoclavicular joints Vertebral articulations Temporomandibular joints Sacroiliac joints Hip joints Knee joints Articulations of footUnmyelinated nerve fibers are abundant in joint capsules and ligaments as well as in the outer part of intraarticular menisci.
These nerve fibers are responsible for pain perception. Damaging the cartilage of joints or the bones and muscles that stabilize the joints can lead to joint dislocations and osteoarthritis. Swimming is a great way to exercise the joints with minimal damage. A joint disorder is termed arthropathy, when involving inflammation of one or more joints the disorder is called arthritis. Most joint disorders involve arthritis, but joint damage by external physical trauma is not termed arthritis. Arthropathies are called polyarticular when involving many joints and monoarticular when involving only a single joint. Arthritis is the leading cause of disability in people over the age of 55. There are many different forms of arthritis; the most common form of arthritis, occurs following trauma to the joint, following an infection of the joint or as a result of aging and the deterioration of articular cartilage. Furthermore, there is emerging evidence that abnormal anatomy may contribute to early development of osteoarthritis.
Other forms of arthritis are rheumatoid arthritis and psoriatic arthritis, which are autoimmune diseases in which the body is attacking itself. Septic arthritis is caused by joint infection. Gouty arthritis is caused by deposition of uric acid crystals in the joint that results in subsequent inflammation. Additionally, there is a less common form of gout, caused by the formation of rhomboidal-shaped crystals of calcium pyrophosphate; this form of gout is known as pseudogout. Temporomandibular joint syndrome involves the jaw joints and can cause facial p
A lymph node or lymph gland is an ovoid or kidney-shaped organ of the lymphatic system, of the adaptive immune system, present throughout the body. They are linked by the lymphatic vessels as a part of the circulatory system. Lymph nodes are major sites of B and T lymphocytes, other white blood cells. Lymph nodes are important for the proper functioning of the immune system, acting as filters for foreign particles and cancer cells. Lymph nodes do not have a detoxification function, dealt with by the liver and kidneys. In the lymphatic system the lymph node is a secondary lymphoid organ. A lymph node is enclosed in a fibrous capsule and is made up of an outer cortex and an inner medulla. Lymph nodes have clinical significance, they become inflamed or enlarged in various diseases which may range from trivial throat infections, to life-threatening cancers. The condition of the lymph nodes is important in cancer staging, which decides the treatment to be used, determines the prognosis; when swollen, inflamed or enlarged, lymph nodes can be hard, tender.
Lymph nodes are oval shaped and range in size from a few millimeters to about 1 -- 2 cm long. Each lymph node is surrounded by a fibrous capsule, which extends inside the lymph node to form trabeculae; the substance of the lymph node is divided into the inner medulla. The cortex is continuous around the medulla except where the medulla comes into direct contact with the hilum. Thin reticular fibers of reticular connective tissue, elastin form a supporting meshwork called a reticulin inside the node. B cells are found in the outer cortex where they are clustered together as follicular B cells in lymphoid follicles and the T cells are in the paracortex; the lymph node is divided into compartments called lymph nodules each consisting of a cortical region of combined follicle B cells, a paracortical region of T cells, a basal part of the nodule in the medulla. The number and composition of follicles can change when challenged by an antigen, when they develop a germinal center. Elsewhere in the node, there are only occasional leukocytes.
As part of the reticular network there are follicular dendritic cells in the B cell follicle and fibroblastic reticular cells in the T cell cortex. The reticular network not only provides the structural support, but the surface for adhesion of the dendritic cells and lymphocytes, it allows exchange of material with blood through the high endothelial venules and provides the growth and regulatory factors necessary for activation and maturation of immune cells. Lymph enters the convex side of the lymph node through multiple afferent lymphatic vessels, flows through spaces called sinuses. A lymph sinus which includes the subcapsular sinus, is a channel within the node, lined by endothelial cells along with fibroblastic reticular cells and this allows for the smooth flow of lymph through them; the endothelium of the subcapsular sinus is continuous with that of the afferent lymph vessel and with that of the similar sinuses flanking the trabeculae and within the cortex. All of these sinuses drain the filtered lymphatic fluid into the medullary sinuses, from where the lymph flows into the efferent lymph vessels to exit the node at the hilum on the concave side.
These vessels are smaller and don't allow the passage of the macrophages so that they remain contained to function within the lymph node. In the course of the lymph, lymphocytes may be activated as part of the adaptive immune response; the lymph node capsule is composed of dense irregular connective tissue with some plain collagenous fibers, from its internal surface are given off a number of membranous processes or trabeculae. They pass inward, radiating toward the center of the node, for about one-third or one-fourth of the space between the circumference and the center of the node. In some animals they are sufficiently well-marked to divide the peripheral or cortical portion of the node into a number of compartments, but in humans this arrangement is not obvious; the larger trabeculae springing from the capsule break up into finer bands, these interlace to form a mesh-work in the central or medullary portion of the node. In these trabecular spaces formed by the interlacing trabeculae is contained the proper lymph node substance or lymphoid tissue.
The node pulp does not, however fill the spaces, but leaves, between its outer margin and the enclosing trabeculae, a channel or space of uniform width throughout. This is termed the subcapsular sinus. Running across it are a number of finer trabeculae of reticular connective tissue, the fibers of which are, for the most part, covered by ramifying cells; the subcapsular sinus is the space between the capsule and the cortex which allows the free movement of lymphatic fluid and so contains few lymphocytes. It is continuous with the similar lymph sinuses; the lymph node contains lymphoid tissue, i.e. a meshwork or fibers called reticulum with white blood cells enmeshed in it. The regions where there are few cells within the meshwork are known as lymph sinus, it is lined by reticular cells and fixed macrophages. The subcapsular sinus has clinical importance as it is the most location where the earliest manifestations of a metastatic carcinoma in a lymph node would be found; the cortex of the lymph node is the outer portion of the node, underneath the capsule and the subcapsular sinus.
It has a deeper part known as the paracortex. The subcapsular sinus drains to the trabecul sinuses, the lymph flows into the medullary sinuses; the outer cortex consists of the B c
Cavitation is a phenomenon in which rapid changes of pressure in a liquid lead to the formation of small vapor-filled cavities, in places where the pressure is low. When subjected to higher pressure, these cavities, called "bubbles" or "voids", collapse and can generate an intense shock wave. Cavitation is a significant cause of wear in some engineering contexts. Collapsing voids that implode near to a metal surface cause cyclic stress through repeated implosion; this results in surface fatigue of the metal causing a type of wear called "cavitation". The most common examples of this kind of wear are to pump impellers, bends where a sudden change in the direction of liquid occurs. Cavitation is divided into two classes of behavior: inertial cavitation and non-inertial cavitation; the process in which a void or bubble in a liquid collapses, producing a shock wave, is called inertial cavitation. Inertial cavitation occurs in nature in the strikes of mantis shrimps and pistol shrimps, as well as in the vascular tissues of plants.
In man-made objects, it can occur in control valves, pumps and impellers. Non-inertial cavitation is the process in which a bubble in a fluid is forced to oscillate in size or shape due to some form of energy input, such as an acoustic field; such cavitation is employed in ultrasonic cleaning baths and can be observed in pumps, etc. Since the shock waves formed by collapse of the voids are strong enough to cause significant damage to moving parts, cavitation is an undesirable phenomenon, it is often avoided in the design of machines such as turbines or propellers, eliminating cavitation is a major field in the study of fluid dynamics. However, it is sometimes useful and does not cause damage when the bubbles collapse away from machinery, such as in supercavitation. Inertial cavitation was first observed in the late 19th century, considering the collapse of a spherical void within a liquid; when a volume of liquid is subjected to a sufficiently low pressure, it may rupture and form a cavity. This phenomenon is coined cavitation inception and may occur behind the blade of a rotating propeller or on any surface vibrating in the liquid with sufficient amplitude and acceleration.
A fast-flowing river can cause cavitation on rock surfaces when there is a drop-off, such as on a waterfall. Other ways of generating cavitation voids involve the local deposition of energy, such as an intense focused laser pulse or with an electrical discharge through a spark. Vapor gases evaporate into the cavity from the surrounding medium; such a low-pressure bubble in a liquid begins to collapse due to the higher pressure of the surrounding medium. As the bubble collapses, the pressure and temperature of the vapor within increases; the bubble collapses to a minute fraction of its original size, at which point the gas within dissipates into the surrounding liquid via a rather violent mechanism which releases a significant amount of energy in the form of an acoustic shock wave and as visible light. At the point of total collapse, the temperature of the vapor within the bubble may be several thousand kelvin, the pressure several hundred atmospheres. Inertial cavitation can occur in the presence of an acoustic field.
Microscopic gas bubbles that are present in a liquid will be forced to oscillate due to an applied acoustic field. If the acoustic intensity is sufficiently high, the bubbles will first grow in size and rapidly collapse. Hence, inertial cavitation can occur if the rarefaction in the liquid is insufficient for a Rayleigh-like void to occur. High-power ultrasonics utilize the inertial cavitation of microscopic vacuum bubbles for treatment of surfaces and slurries; the physical process of cavitation inception is similar to boiling. The major difference between the two is the thermodynamic paths that precede the formation of the vapor. Boiling occurs when the local temperature of the liquid reaches the saturation temperature, further heat is supplied to allow the liquid to sufficiently phase change into a gas. Cavitation inception occurs when the local pressure falls sufficiently far below the saturated vapor pressure, a value given by the tensile strength of the liquid at a certain temperature. In order for cavitation inception to occur, the cavitation "bubbles" need a surface on which they can nucleate.
This surface can be provided by the sides of a container, by impurities in the liquid, or by small undissolved microbubbles within the liquid. It is accepted that hydrophobic surfaces stabilize small bubbles; these pre-existing bubbles start to grow unbounded when they are exposed to a pressure below the threshold pressure, termed Blake's threshold. The vapor pressure here differs from the meteorological definition of vapor pressure, which describes the partial pressure of water in the atmosphere at some value less than 100% saturation. Vapor pressure as relating to cavitation refers to the vapor pressure in equilibrium conditions and can therefore be more defined as the equilibrium vapor pressure. Non-inertial cavitation is the process in which small bubbles in a liquid are forced to oscillate in the presence of an acoustic field, when the intensity of the acoustic field is insufficient to cause total bubble collapse; this form of cavitation causes less erosion than inertial cavitation, is used for the cleaning of delicate materials, such as silicon wafers.
Hydrodynamic cavitation describes the process of vaporisation, bubble generation and bubble implosion which occurs in a flowing liquid as a result of a decrease and su