Primary drying raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2025-11-21 and is reviewed periodically as new material appears.
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.
Freeze-drying is distinct from simple evaporation and from spray drying. Evaporation removes water at temperatures above freezing, while spray drying rapidly dries droplets in a heated gas stream. Lyophilization avoids high temperatures, which can be useful for heat-sensitive materials such as proteins, vaccines, and some foods. The porous cake produced by sublimation dissolves or rehydrates more quickly than a dense dried mass. Not all materials tolerate freezing or the pH shifts that can occur as solutes concentrate during ice formation.
Lyophilization removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and fixes the structure of the sample. After freezing, primary drying lowers pressure so ice changes directly to vapor without passing through a liquid phase. Secondary drying then removes bound water that remains after ice sublimation. The result is a dry, porous solid that often retains its original shape.
| Property | Value | Notes |
|---|---|---|
| Common name | Freeze-drying | Process removes water by sublimation under vacuum. |
| Typical primary drying shelf temperature | -40 C to -10 C | Set below the formulation's collapse temperature. |
| Typical chamber pressure | 0.05-0.3 mbar | Low pressure allows ice to sublime below its triple point. |
| Water content after drying | 0.5-3% by weight | Higher values may reduce storage stability for some materials. |
| Key thermal parameter | Collapse temperature | Measured by freeze-drying microscopy or differential scanning calorimetry. |
A typical cycle begins with freezing, sometimes including an annealing step to control ice crystal size. Freezing conditions influence the pore network that later allows vapor escape. During primary drying, shelf temperature and chamber pressure are set so heat enters the product while its temperature stays below the collapse or eutectic point. Secondary drying then raises the shelf temperature to desorb bound water and lower residual moisture. Cycle design depends on formulation, fill volume, container type, and equipment capability.
The physics of lyophilization couples heat transfer, mass transfer, and phase behavior. Sublimation requires a vapor pressure difference between the ice front and the chamber, and the dried layer adds resistance to vapor flow. Amorphous formulations are characterized by a glass transition temperature of the maximally freeze-concentrated solute, often denoted Tg'. Crystalline bulking agents can provide structure, while amorphous excipients stabilize labile components. Open questions remain about spatial heterogeneity, edge effects, and how laboratory cycles scale to production.
Lyophilization is a drying process in which a solvent, usually water, is removed from a frozen material by sublimation under reduced pressure. The material is first solidified, then placed under vacuum so that ice transitions directly to vapor without a bulk liquid phase. This approach suits heat-sensitive substances that would degrade during conventional evaporation. Primary drying removes unbound ice, while secondary drying reduces water that remains adsorbed to the solid matrix. The result is a porous, lightweight solid that can be reconstituted later.
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.
== Transportation units == Prior to the 2018 reforms, the People's Armed Police Transportation Corps (Chinese: 武警交通部队) was its own independent corps under the dual command of the PAP and the Ministry of Transport. During the 2018 reforms, the Transportation Corps was reorganised into part of the 1st and 2nd mobile corps. The mission of Transport units of the People's Armed Police is to conduct disaster relief and emergency repair on highways, bridges, tunnels, seaports railways and airports, security to construction projects related to national security along with law enforcement duties on highways in border regions.
=== Microtemplate polymerization === The addition of a monomer precursor solution and crosslinking agent to a microtemplate, or mold-type device, can initiate polymerization and the formation of nanogels. This method can be used to create nanogels in specific shapes and load them with various small molecules. Lithographic microtemplate polymerization is a similar process that uses a photoinitiator and light to trigger the formation of nanogels. Lithographic microtemplate polymerization can produce smaller nanogels on a length scale of <200 nm, which has a higher resolution compared to microtemplate polymerization that does not require a photoinitiator.
1956: 1956 Summer Olympics – USSR-Hungary Blood in the Water match following the Hungarian Revolution and the Soviet invasion of Hungary 1969: 1969 World Ice Hockey Championships – USSR-Czechoslovakia following the 1968 Soviet invasion of Czechoslovakia 1972: 1972 Summer Olympics – The USSR defeats the United States in men's basketball in a controversial gold medal game 1972: Canada–USSR Summit Series – Canada defeats the Soviet Union in this best-on-best eight-game series 1972: 1972 World Chess Championship Fischer (USA) – Spassky (USSR) – Bobby Fischer beats Spassky in this championship held in Reykjavik, Iceland 1980: Miracle on Ice – The United States upsets the favoured USSR at the 1980 Winter Olympics 1980: 1980 Summer Olympics boycott – by the United States 1984: 1984 Summer Olympics boycott – by the Soviet Union
There are two essentially different kinds of ornithology: systematic or scientific, and popular. The former deals with the structure and classification of birds, their synonymies, and technical descriptions. The latter treats of their habits, songs, nesting, and other facts pertaining to their life histories. This early idea that the study of living birds was merely recreation held sway until ecological theories became the predominant focus of ornithological studies. The study of birds in their habitats was particularly advanced in Germany with bird ringing stations established as early as 1903. By the 1920s, the Journal für Ornithologie included many papers on the behaviour, ecology, anatomy, and physiology, many written by Erwin Stresemann. Stresemann changed the editorial policy of the journal, leading both to a unification of field and laboratory studies and a shift of research from museums to universities. Ornithology in the United States continued to be dominated by museum studies of morphological variations, species identities, and geographic distributions, until it was influenced by Stresemann's student Ernst Mayr. In Britain, some of the earliest ornithological works that used the word ecology appeared in 1915. The Ibis, however, resisted the introduction of these new methods of study, and no paper on ecology appeared until 1943. The work of David Lack on population ecology was pioneering. Newer quantitative approaches were introduced for the study of ecology and behaviour, and this was not readily accepted. For instance, Claud Ticehurst wrote:
== Comorbidity == Diabetes patients' comorbidities have a significant impact on medical expenses and related costs. It has been demonstrated that patients with diabetes are more likely to experience respiratory, urinary tract, and skin infections, develop atherosclerosis, hypertension, and chronic kidney disease, putting them at increased risk of infection and complications that require medical attention. Patients with diabetes mellitus are more likely to experience certain infections, such as COVID-19, with prevalence rates ranging from 5.3 to 35.5%. Maintaining adequate glycemic control is the primary goal of diabetes management since it is critical to managing diabetes and preventing or postponing such complications. People with type 1 diabetes have higher rates of autoimmune disorders than the general population. An analysis of a type 1 diabetes registry found that 27% of the 25,000 participants had other autoimmune disorders. Between 2% and 16% of people with type 1 diabetes also have celiac disease.
Sources: en.wikipedia.org
In a passage describing the challenges of "boiling an egg", for instance, the reader is not given any clue that the original Japanese text discussed a speciality of Kyoto-style cuisine called koya dofu (高野豆腐), a freeze dried tofu dish named after the Koyasan region from which it originates. In contrast to the symbolism of Kyoto-style cuisine as authentic Japanese fare, Tanizaki disparages Kobe as "foreign" including items like liver sausage from a German butcher. Of Tanazaki's characters, Louise, a prostitute involved with Kaname, is the most strongly associated with Kobe fare. Though Misako's consumption of the Kobe style food is alluded to from time to time, Misako herself is more clearly associated with the eastern Japanese fare of Tokyo.
==== Nigeria ==== In February 2021, Zipline announced a plan to construct three distribution centers in Kaduna State, Nigeria. These distribution centers would have ultra-cold storage that is capable of safely storing COVID-19 vaccines, for which health facilities in the state could then place on-demand orders without needing ultra-cold storage of their own. The state also intends to use Zipline's service to transport other health products, including blood, medication, and routine vaccines. In May 2021, Zipline announced a similar agreement with Cross River State. In February 2022, Zipline announced another agreement with Bayelsa State. The first hub opened in Kaduna state in an undisclosed location on June 4, 2022.
Aldehyde tags were first inserted into the modified sulfatase motif peptide for proteins of interest in 2007. Since then, similar usage of aldehydes and ketones as chemical reporters in bioorthogonal applications has been demonstrated in self-assembly of cell-lysing drugs, the targeting of proteins, as well as glycans and the preparation of heterobifunctional fusion proteins.
It also identified five areas of focus: expanding plant-based menu options; shifting to reusable packaging; investing in regenerative agriculture, reforestation, forest conservation and water replenishment; better ways to manage waste; and more eco-friendly stores, operations, manufacturing, and delivery.
Sources: en.wikipedia.org
While most historians trace its origins to the period immediately following World War II, others argue that it began with the October Revolution in Russia in 1917 when the Bolsheviks took power. In 1919 Lenin stated that his new state was surrounded by a "hostile capitalist encirclement", and he viewed diplomacy as a weapon that should be used in order to keep the Soviet Union's enemies divided. He began with a new Communist International ("Comintern"), based in Moscow, which was designed to plan for revolutionary upheavals abroad. It was ineffective—Communist uprisings all failed in Germany, Hungary and elsewhere. Historian Max Beloff argues that the Soviets saw "no prospect of permanent peace", with the 1922 Soviet Constitution proclaiming:
=== Skin cancers === MCH has been identified in both melanoma and squamous cell carcinoma cell lines. However, pro-MCH, a precursor to MCH, has not been found in melanocytes, keratinocytes, or fibroblasts, which might indicate MCH might be brought into these cells by macrophages as part of the immune response. More research is needed to fully determine and understand any relationship between MCH and possible immune responses in skin.
Considered radicals by another moderate current of the PCC, they used terrorism to intimidate authorities of the prison system and were withdrawn from leadership in November 2002, when the leadership was taken over by the current leader of the organization, Marcos "Marcola" Willians Herbas Camacho. Marcola would eventually order the deaths of Geleião and Cesinha for having testified to the police, as well as for allegedly leaving the faction and creating a splinter group called the "Terceiro Comando da Capital" (Third Capital Command, TCC), which is now considered to be defunct.
Sources: en.wikipedia.org
Primary drying removes ice by sublimation at low pressure and low shelf temperature. Secondary drying removes bound water by raising the shelf temperature, often under the same vacuum. The two stages differ in the water state being removed.
Freezing determines ice crystal size, pore structure, and the concentration of solutes in remaining liquid. Faster freezing generally creates smaller ice crystals and a denser dried matrix. These features affect drying rate and reconstitution behavior.
Lyophilization reduces water content but usually leaves a small amount of water in the dried material. Some water remains bound to solids or trapped in the dried matrix. Very low water targets can require extended secondary drying, which may alter product stability.
Lyophilization relies on sublimation, so water moves from solid ice to vapor without becoming liquid. The material is frozen, pressure is reduced, and controlled heat is supplied. Vapor is captured on a cold condenser, leaving a dry porous solid.