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High frequency (HF) is the ITU designation [1] [2] for the band of radio waves with frequency between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters (ten to one hundred meters).
Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome caused by an impairment in the heart's ability to fill with and pump blood. Although symptoms vary based on which side of the heart is affected, HF typically presents with shortness of breath , excessive fatigue , and bilateral leg swelling . [ 3 ]
Solid HF consists of zig-zag chains of HF molecules. The HF molecules, with a short covalent H–F bond of 95 pm length, are linked to neighboring molecules by intermolecular H–F distances of 155 pm. [4] Liquid HF also consists of chains of HF molecules, but the chains are shorter, consisting on average of only five or six molecules. [5]
Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water.Solutions of HF are colorless, acidic and highly corrosive.A common concentration is 49% (48-52%) but there are also stronger solutions (e.g. 70%) and pure HF has a boiling point near room temperature.
Hafnium, symbol Hf, a chemical element; Hartree–Fock method, a calculation scheme in the field of computational chemistry; Hydrogen fluoride, HF, a diatomic compound which can dissolve in water to form hydrofluoric acid, a highly corrosive solution; Hydrofluoric acid, HF (aq), a solution of hydrogen fluoride (HF) in water
The idea to give each band a number, in which the number is the logarithm of the approximate geometric mean of the upper and lower band limits in Hz, originated with B. C. Fleming-Williams, who suggested it in a letter to the editor of Wireless Engineer in 1942. For example, the approximate geometric mean of band 7 is 10 MHz, or 10 7 Hz. [14]
Meaning h: hr / hours H: histamine or its receptors (if with subscripts) hemagglutinin: H x: history: HA ; H/A hypertonia arterialis headache calcium hydroxyapatite HAA: hepatitis-associated antigen or #History As Above HAART: highly active antiretroviral therapy HACA: human anti-chimeric antibody: HACE: High-altitude cerebral edema: HACEK
Grundig Satellit 400 solid-state, digital shortwave receiver, c. 1986 [1]. Shortwave radio is radio transmission using radio frequencies in the shortwave bands (SW). There is no official definition of the band range, but it always includes all of the high frequency band (HF), which extends from 3 to 30 MHz (approximately 100 to 10 metres in wavelength).