A practical reference on Collapse temperature: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2025-10-02. Anything still debated is marked as such rather than presented as settled.
Lyophilization is a dehydration process that removes water from a frozen material by sublimation under low pressure. The material is first frozen to convert liquid water into ice. Next, the pressure is reduced below the triple point of water so that ice changes directly into vapor without passing through a liquid phase. This step is called primary drying. The result is a porous solid or cake that retains the original shape of the frozen solution.
After primary drying, secondary drying removes water that remains bound to the material. This stage raises the shelf temperature while maintaining low pressure, which encourages desorption of unfrozen water. Residual moisture can be reduced to a low percentage, improving stability for many products. The process parameters, including freezing rate, shelf temperature, and chamber pressure, influence the final pore structure and reconstitution behavior. Control of these variables helps prevent collapse or meltback during drying.
The process usually has three stages: freezing, primary drying, and secondary drying. Freezing sets the ice crystal structure and can determine pore size in the final cake. Primary drying removes free ice by sublimation at low pressure and low shelf temperature. Secondary drying removes bound water by raising the shelf temperature, although some water may remain as part of the solid. Cycle parameters depend on formulation, fill volume, vial type, and equipment performance.
The physical chemistry of freezing influences whether a formulation forms an amorphous glass or a crystalline solid. Amorphous systems can collapse if product temperature rises above the glass transition temperature of the freeze concentrate. Crystalline systems may show eutectic melting, where ice and solute melt together at a fixed temperature. Formulators add bulking agents, lyoprotectants, and buffers to preserve structure and biological activity. The optimum cycle keeps product temperature below critical thresholds during primary drying while allowing efficient sublimation.
| Property | Value | Notes |
|---|---|---|
| Common synonyms | Freeze-drying, lyophilisation | Lyophilization is the American spelling; lyophilisation is British |
| Primary drying mechanism | Sublimation of ice | Occurs under vacuum below the triple point |
| Typical chamber pressure | 0.05-0.5 mbar | Range depends on product and equipment |
| Typical shelf temperature during freezing | -40 to -20 °C | Lower temperatures may be used for labile products |
| Resulting product form | Porous cake or powder | Appearance depends on formulation and cycle |
The physics of freeze-drying couples heat transfer, mass transfer, and phase change. Heat supplied through the shelf must reach the sublimation front without melting the ice or degrading the product. Water vapor then travels through the already dried layer and leaves the chamber, where low pressure and cold traps keep it from returning. The dried layer acts as a resistance to vapor flow, so drying rate changes as the front recedes. Open questions remain about how pore structure and formulation heterogeneity affect drying uniformity at larger scales.
Lyophilization removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and concentrates dissolved solids. Primary drying then lowers chamber pressure so ice changes directly into vapor without passing through a liquid phase. Secondary drying raises the shelf temperature to remove bound water that remains after ice sublimation. The result is a dry, porous structure that can be reconstituted later.
Formulation composition influences whether freeze-drying produces an intact cake or a collapsed mass. Excipients such as sugars and polymers can raise the collapse temperature and provide bulk during drying. The critical temperature for primary drying is often the collapse temperature or the glass transition temperature of the maximally concentrated phase. If the product temperature exceeds this threshold, the frozen matrix may soften and lose structure. Established practice therefore links shelf temperature and chamber pressure to the formulation's thermal properties.
Freezing determines ice crystal structure and pore size, which affect drying speed and product uniformity. Rapid freezing creates small crystals, while slow freezing creates larger crystals and often faster sublimation. During primary drying, chamber pressure is held below the vapor pressure of ice, and shelf temperature supplies heat for sublimation. The ice front recedes, leaving a porous matrix. Thermal limits such as collapse and eutectic temperatures set safe boundaries for formulation. These limits vary with solute composition and concentration.
Secondary drying removes bound water that remains after ice sublimation. Shelf temperature is raised gradually while pressure remains low, reducing water content to a target range. Over-drying can cause brittleness or electrostatic issues, while under-drying affects stability. The endpoint is often judged by pressure rise tests, temperature measurements, or water content analysis. Scale-up depends on matching heat and mass transfer across equipment sizes. Small changes in shelf temperature or pressure can alter cycle length substantially.
==== Exact analytical solutions to the SIR model ==== In 2014, Harko and coauthors derived an exact so-called analytical solution (involving an integral that can only be calculated numerically) to the SIR model. In the case without vital dynamics setup, for
In 2004, a special issue of The International Journal of Sociology and Social Policy was published that was edited by Steven P. Schacht, who participated in the SSSP session. The special issue contained ten articles analyzing his research and his multiple contributions as a social activist and scholar. The authors of these articles call for sociologists and others to move beyond criticism of Humphrey's research methodologies in the tearoom study, and instead to focus on his pioneering contributions to the study of sexuality, participant-observation as method, development of sociological theory, and his work as a social activist and advocate for marginalized sexual identities.
==== Reagent coflow prior to droplet formation ==== Reagents can be added at the time of droplet formation through a "co-flow" geometry. Reagent streams are pumped in separate channels and join at the interface with a channel containing the continuous phase, which shears and creates droplets containing both reagents. By changing the flow rates in reagent channels, reagent ratios within a droplet can be controlled.
=== Vertebrates === Vertebrates were once thought to be unable to perform this cycle because there was no evidence of its two key enzymes, isocitrate lyase and malate synthase. However, some research suggests that this pathway may exist in some, if not all, vertebrates.
Sources: en.wikipedia.org
For high-risk patients (white blood cell count >10,000/μL), treatment usually entails ATRA plus ATO along with the addition of chemotherapy (such as idarubicin) during induction to rapidly control leukocytosis and reduce early death and relapse risk. Effectiveness appears similar to Realgar/Indigo naturalis, which can be taken by mouth and is less expensive but is less available. It works by encouraging the proteosome breakdown of retinoic acid receptor alpha, by moving the protein on to the nuclear matrix and increasing ubiquitination. This use was approved for leukemia treatment in the United States in 2000. A liquid form of arsenic trioxide that can be given by mouth, (Oral-ATO; ARSENOL®) for the treatment of acute promyelocytic leukaemia.
Each neurotransmitter has very specific degradation pathways at regulatory points, which may be targeted by the body's regulatory system or medication. Cocaine blocks a dopamine transporter responsible for the reuptake of dopamine. Without the transporter, dopamine diffuses much more slowly from the synaptic cleft and continues to activate the dopamine receptors on the target cell.
=== Reconstitution in exile === In January 1921, Russian émigrés meeting in Warsaw re-established the organization under the name People's Union for the Defense of the Motherland and Freedom. The reconstituted organization sought to continue anti-Bolshevik activity from abroad and to rebuild an underground network inside Soviet territory. Between 1921 and 1923, the People's Union engaged in underground and subversive activities directed against the Bolshevik regime. Volunteers and operatives were sent into the Soviet Union in an effort to organize armed detachments, establish clandestine cells, recruit supporters, and attempt to provoke a broader anti-Bolshevik uprising.
Women are allowed to enter the Paris stock exchange and speculate. 1970: The concept of "head of the household" is abolished. Equality between spouses in managing the household is established. Parental authority is created. 1971: Introduction of maternity leave compensated at 90%. 1972: A law introduces the principle of equal pay between men and women; the first in a series of laws on the subject that are rarely enforced. Women are admitted to École Polytechnique. 1975: Law banning all discrimination in the civil service. Simone Veil passed a law decriminalizing and regulating voluntary termination of pregnancy (abortion). A husband can no longer read his wife's correspondence or control her relationships. All higher education is accessible to women. 1977: Abolition of the single wage allowance. 1982: Wives of tradesmen and artisans can choose between three statuses: collaborating spouse, employee, or partner. 1983: Law on pay equality between men and women, very poorly enforced. 1984: Parental leave is made available to either parent. 1986: Ministerial circular promoting the feminization of job titles: artisane, écrivaine, etc. 1987: Loosening of restrictions on night work. 1992: Law against sexual harassment. 2001: Strengthening of the 1983 law on professional equality. 2005: New law on professional equality, with no binding criteria or penalties in case of non-compliance. 2006: Law on gender equality in education. 2006: Domestic violence prevention.
Genetic gingival enlargement presents in children with firm, fibrotic, generalized gingival overgrowth beginning around tooth eruption, often requiring surgical management. These cases are identified by tissue overgrowth-related pseudopocket formation and generally intact periodontal attachment.
Sources: en.wikipedia.org
Vapour pressure is the pressure of a vapour in thermodynamic equilibrium with its condensed phases in a closed system. All liquids and solids have a tendency to evaporate into a gaseous form, and all gases have a tendency to condense back to their liquid or solid form. The atmospheric pressure boiling point of a liquid (also known as the normal boiling point) is the temperature at which the vapor pressure equals the ambient atmospheric pressure. With any incremental increase in that temperature, the vapor pressure becomes sufficient to overcome atmospheric pressure and lift the liquid to form vapour bubbles inside the bulk of the substance. Bubble formation deeper in the liquid requires a higher pressure, and therefore higher temperature, because the fluid pressure increases above the atmospheric pressure as the depth increases. The vapor pressure that a single component in a mixture contributes to the total pressure in the system is called partial vapor pressure.
Increases levels of dehydroepiandrosterone (DHEA) directly by action on the fetal adrenal gland, and indirectly via the mother's pituitary gland. DHEA has a role in preparing for and stimulating cervical contractions. Increases prostaglandin availability in uteroplacental tissues. Prostaglandins activate cervical contractions. Prior to parturition it may have a role inhibiting contractions, through increasing cAMP levels in the myometrium. In culture, trophoblast CRH is inhibited by progesterone, which remains high throughout pregnancy. Its release is stimulated by glucocorticoids and catecholamines, which increase prior to parturition lifting this progesterone block.
== History == Historically this equation arose as a variant on the Prony equation; this variant was developed by Henry Darcy of France, and further refined into the form used today by Julius Weisbach of Saxony in 1845. Initially, data on the variation of fD with velocity was lacking, so the Darcy–Weisbach equation was outperformed at first by the empirical Prony equation in many cases. In later years it was eschewed in many special-case situations in favor of a variety of empirical equations valid only for certain flow regimes, notably the Hazen–Williams equation or the Manning equation, most of which were significantly easier to use in calculations. However, since the advent of the calculator, ease of calculation is no longer a major issue, and so the Darcy–Weisbach equation's generality has made it the preferred one.
=== Safety and toxicology === A number of cyanobacteria, of which spirulina is one, produce toxins such as microcystins. Some spirulina supplements have been found to be contaminated with microcystins, albeit at levels below the limit set by the Oregon Health Department. Microcystins can cause gastrointestinal upset, such as diarrhea, flatulence, headache, muscle pain, facial flushing, and sweating. Chronic exposure may lead to liver damage. The effects of chronic exposure to even low levels of microcystins are a concern due to the risk of toxicity to several organ systems. These toxic compounds are not produced by spirulina itself, but can occur if spirulina batches are contaminated with other, toxin-producing, blue-green algae. Because spirulina products are marketed as a dietary supplement, such products are made to the standards of processing and chemical purity of the manufacturer. Accordingly, spirulina supplements are regarded only as "possibly safe", provided they are free of microcystin contamination, and "likely unsafe" (especially for children) if contaminated. Public-health researchers have raised the concern that consumers cannot be certain that spirulina and other blue-green algae supplements are free of contamination. In 2016, a review by Health Canada of available literature found that spirulina products contained varying levels of microcystins. Health Canada restricts microcystin-LR levels in products containing cyanobacteria to 0.02 μg per kilogram of body weight per day in finished products, or a maximum of 1 part per million in raw materials.
Sources: en.wikipedia.org
Lyophilization removes water by sublimation from a frozen material, while evaporation changes liquid water into vapor. The low-pressure freezing step avoids the liquid phase and can preserve heat-sensitive structures.
Vacuum lowers the pressure below the triple point of water, allowing ice to sublimate directly into vapor. It also helps remove water vapor from the product chamber and shortens primary drying.
Many aqueous solutions and suspensions can be freeze-dried, but some formulations collapse or do not form a stable cake. The process requires careful formulation and cycle development.
The main change is sublimation, in which ice becomes water vapor without melting into liquid water. This occurs when the chamber pressure is held below the vapor pressure of ice while mild heat is supplied. The result is a dry, porous solid that retains much of its original shape.