A placebo is an inert substance or treatment, designed to have no therapeutic value. Common placebos include inert tablets, inert injections, sham surgery, other procedures. In general, placebos can affect how patients perceive their condition and encourage the body's chemical processes for relieving pain and a few other symptoms, but have no impact on the disease itself. Improvements that patients experience after being treated with a placebo can be due to unrelated factors, such as regression to the mean; the use of placebos in clinical medicine raises ethical concerns if they are disguised as an active treatment, as this introduces dishonesty into the doctor–patient relationship and bypasses informed consent. While it was once assumed that this deception was necessary for placebos to have any effect, there is now evidence that placebos can have effects when the patient is aware that the treatment is a placebo. In drug testing and medical research, a placebo can be made to resemble an active medication or therapy so that it functions as a control.
In a clinical trial any change in the placebo arm is known as the placebo response, the difference between this and the result of no treatment is the placebo effect. Some researchers now recommend comparing the experimental treatment with an existing treatment when possible, instead of a placebo; the idea of a placebo effect—a therapeutic outcome derived from an inert treatment—was discussed in 18th century psychology but became more prominent in the 20th century. An influential 1955 study entitled The Powerful Placebo established the idea that placebo effects were clinically important, were a result of the brain's role in physical health. A 1997 reassessment found no evidence of any placebo effect in the source data, as the study had not accounted for regression to the mean. Placebo is Latin, it was used as a name for the Vespers in the Office of the Dead, taken from a phrase used in it, a quote from the Vulgate's Psalm 114:9. From that, a singer of placebo became associated with someone who falsely claimed a connection to the deceased to get a share of the funeral meal, hence a flatterer, so a deceptive act to please.
The American Society of Pain Management Nursing define a placebo as "any sham medication or procedure designed to be void of any known therapeutic value". In a clinical trial, a placebo response is the measured response of subjects to a placebo, it is part of the recorded response to any active medical intervention. Any measurable placebo effect is termed either objective or subjective. Placebos can improve patient-reported outcomes such as nausea; this effect is unpredictable and hard to measure in the best conducted trials. For example, if used to treat insomnia, placebos can cause patients to perceive that they are sleeping better, but do not improve objective measurements of sleep onset latency. A 2001 Cochrane Collaboration meta-analysis of the placebo effect looked at trials in 40 different medical conditions, concluded the only one where it had been shown to have a significant effect was for pain. By contrast, placebos do not appear to affect the actual diseases, or outcomes that are not dependent on a patient's perception.
One exception to the latter is Parkinson's disease, where recent research has linked placebo interventions to improved motor functions. Measuring the extent of the placebo effect is difficult due to confounding factors. For example, a patient may feel better after taking a placebo due to regression to the mean, it is harder still to tell the difference between the placebo effect and the effects of response bias, observer bias and other flaws in trial methodology, as a trial comparing placebo treatment and no treatment will not be a blinded experiment. In their 2010 meta-analysis of the placebo effect, Asbjørn Hróbjartsson and Peter C. Gøtzsche argue that "even if there were no true effect of placebo, one would expect to record differences between placebo and no-treatment groups due to bias associated with lack of blinding."Hróbjartsson and Gøtzsche concluded that their study "did not find that placebo interventions have important clinical effects in general." Jeremy Howick has argued that combining so many varied studies to produce a single average might obscure that "some placebos for some things could be quite effective."
To demonstrate this, he participated in a systematic review comparing active treatments and placebos using a similar method, which generated a misleading conclusion that there is "no difference between treatment and placebo effects". A review published in JAMA Psychiatry found that, in trials of antipsychotic medications, the change in response to receiving a placebo had increased between 1960 and 2013; the review's authors identified several factors that could be responsible for this change, including inflation of baseline scores and enrollment of fewer ill patients. Another analysis published in Pain in 2015 found that placebo responses had increased in neuropathic pain clinical trials conducted in the United States from 1990 to 2013; the researchers suggested that this may be because such trials have "increased in study size and length" during this time period. Children seem to have greater response than adults to placebos; some studies have investigated the use of placebos where the patient is ful
XHNM-FM 98.1 FM is a radio station in Aguascalientes, Mexico located in Jesús María. It is owned by the state government of Aguascalientes through its Radio y Televisión de Aguascalientes division and is the sister station to XHRTA-FM 92.7 and XHCGA-TDT 26. XENM-AM 1320 signed on October 12, 1973, it was known as Radio Casa de la Cultura changing its name to Radio Instituto Cultural de Aguascalientes, La Voz del Estado, Radio Solidaridad. It was known in the early 2010s as "La Estación". In 2007, its daytime power was raised from 1 kW to 6; the new FM station signed on in August 2015. At that time, the station changed its name from "La Estación" to "Teleradio", with a simulcast of the audio of many XHCGA programs. XHNM-FM is located at a different transmitter site from that used by XENM-AM; the Tu Estación name and programming moved to 92.7 XHRTA-FM in early 2018, 98.1 became Alternativa
Metal–organic frameworks are a class of compounds consisting of metal ions or clusters coordinated to organic ligands to form one-, two-, or three-dimensional structures. They are a subclass of coordination polymers, with the special feature that they are porous; the organic ligands included are sometimes referred to as "struts", one example being 1,4-benzenedicarboxylic acid. More formally, a metal–organic framework is a coordination network with organic ligands containing potential voids. A coordination network is a coordination compound extending, through repeating coordination entities, in one dimension, but with cross-links between two or more individual chains, loops, or spiro-links, or a coordination compound extending through repeating coordination entities in two or three dimensions. In some cases, the pores are stable during elimination of the guest molecules and could be refilled with other compounds; because of this property, MOFs are of interest for the storage of gases such as hydrogen and carbon dioxide.
Other possible applications of MOFs are in gas purification, in gas separation, in catalysis, as conducting solids and as supercapacitors. The synthesis and properties of MOFs constitute the primary focus of the discipline called reticular chemistry. In contrast to MOFs, covalent organic framework are made from light elements with extended structures. MOFs are composed of two major components: a metal ion or cluster of metal ions and an organic molecule called a linker. For this reason, the materials are referred to as hybrid organic–inorganic materials; the organic units are mono-, di-, tri-, or tetravalent ligands. The choice of metal and linker dictates the structure and hence properties of the MOF. For example, the metal's coordination preference influences the size and shape of pores by dictating how many ligands can bind to the metal and in which orientation. To describe and organize the structures of MOFs, a system of nomenclature has been developed. Subunits of a MOF, called secondary building units, can be described by topologies common to several structures.
Each topology called a net, is assigned a symbol, consisting of three lower-case letters in bold. MOF-5, for example, has a pcu net; the database of net structures can be found at the Reticular Chemistry Structure Resource. Attached to the SBUs are bridging ligands. For MOF's, typical bridging ligands are di- and tricarboxylic acids; these ligands have rigid backbones. Examples are benzene-1,4-dicarboxylic acid (BDC or teraphthalic acid, biphenyl-4,4'-dicarboxylic acid, the tricarboxylic acid trimesic acid; the study of MOFs developed from the study of zeolite. Except for the use of preformed ligands, MOFs and zeolites are produced exclusively by hydrothermal or solvothermal techniques, where crystals are grown from a hot solution. In contrast with zeolites, MOFs are constructed from bridging organic ligands that remain intact throughout the synthesis. Zeolite synthesis makes use of a "template". Templates are ions. Typical templating ions are quaternary ammonium cations. In MOFs, the framework is templated by the organic ligands.
A templating approach, useful for MOFs intended for gas storage is the use of metal-binding solvents such as N,N-diethylformamide and water. In these cases, metal sites are exposed when the solvent is evacuated, allowing hydrogen to bind at these sites. Since ligands in MOFs bind reversibly, the slow growth of crystals allows defects to be redissolved, resulting in a material with millimeter-scale crystals and a near-equilibrium defect density. Solvothermal synthesis is useful for growing crystals suitable to structure determination, because crystals grow over the course of hours to days. However, the use of MOFs as storage materials for consumer products demands an immense scale-up of their synthesis. Scale-up of MOFs has not been studied, though several groups have demonstrated that microwaves can be used to nucleate MOF crystals from solution; this technique, termed "microwave-assisted solvothermal synthesis", is used in the zeolite literature, produces micron-scale crystals in a matter of seconds to minutes, in yields similar to the slow growth methods.
A solvent-free synthesis of a range of crystalline MOFs has been described. The metal acetate and the organic proligand are mixed and ground up with a ball mill. Cu32 can be synthesised in this way in quantitative yield. In the case of Cu32 the morphology of the solvent free synthesised product was the same as the industrially made Basolite C300, it is thought that localised melting of the components due to the high collision energy in the ball mill may assist the reaction. The formation of acetic acid as a by-product in the reactions in the ball mill may help in the reaction having a solvent effect in the ball mill. A recent advancement in the solvent-free preparation of MOF films and composites is their synthesis by chemical vapor deposition; this process, MOF-CVD, consist of two steps. In a first step, metal oxide precursor layers are deposited. In the second step, these precursor layers are exposed to sublimed ligand molecules, that induce a phase transformation to the MOF crystal lattice. Formation of water during this reaction plays a crucial role in directing the transformation.
This process was succe