関: hertz、Hertz

WordNet

German physicist who with James Franck proved the existence of the stationary energy states postulated by Bohr (1887-1975) (同)Gustav Hertz, Gustav Ludwig Hertz
German physicist who was the first to produce electromagnetic waves artificially (1857-1894) (同)Heinrich Hertz, Heinrich Rudolph Hertz
the unit of frequency; one hertz has a periodic interval of one second (同)Hz, cycle per second, cycles/second, cps, cycle
the 8th letter of the Roman alphabet (同)h

PrepTutorEJDIC

hertz
ヘルツ(毎秒1サイクルに相当する周波数の単位;{略}Hz)
hydrogenの化学記号
鉛筆の硬度 / 《俗》heroin

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/08/31 13:24:13」(JST)

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This article is about the unit of frequency, named after physicist Heinrich Hertz. For rental cars, see The Hertz Corporation. For others, see Hertz (disambiguation).

"Hz" and "MHz" (MHZ) redirect here. For other uses, see HZ (disambiguation) or MHZ (disambiguation).

"Megahertz" redirects here. For the racehorse, see Megahertz (horse).

Lights flash at frequency f = 0.5 Hz (Hz = hertz), 1.0 Hz or 2.0 Hz, where Hz means flashes per second. T is the period and T = s (s = seconds) means that is the number of seconds per flash. T and f are each other's reciprocal: f = 1/T and T = 1/f.

The hertz (symbol Hz) is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon.^[1] One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications, such as the frequency of musical tones. The word "hertz" is named for Heinrich Rudolf Hertz, who was the first to conclusively prove the existence of electromagnetic waves.

Definition

The hertz is equivalent to cycles per second.^[2] In defining the second, the CIPM declared that "the standard to be employed is the transition between the hyperfine levels F = 4, M = 0 and F = 3, M = 0 of the ground state 2S_1/2 of the cesium 133 atom, unperturbed by external fields, and that the frequency of this transition is assigned the value 9 192 631 770 hertz"^[3] thereby effectively defining the hertz and the second simultaneously.

In English, "hertz" is also used as the plural form.^[4] As an SI unit, Hz can be prefixed; commonly used multiples are kHz (kilohertz, 10³ Hz), MHz (megahertz, 10⁶ Hz), GHz (gigahertz, 10⁹ Hz) and THz (terahertz, 10¹² Hz). One hertz simply means "one cycle per second" (typically that which is being counted is a complete cycle); 100 Hz means "one hundred cycles per second", and so on. The unit may be applied to any periodic event—for example, a clock might be said to tick at 1 Hz, or a human heart might be said to beat at 1.2 Hz. The "frequency" (activity) of aperiodic or stochastic events, such as radioactive decay, is expressed in becquerels.

Even though angular velocity, angular frequency and hertz all have the dimensions of 1/s, angular velocity and angular frequency are not expressed in hertz,^[5] but rather in an appropriate angular unit such as radians per second. Thus a disc rotating at 60 revolutions per minute (rpm) is said to be rotating at either 2π rad/s or 1 Hz, where the former measures the angular velocity and the latter reflects the number of complete revolutions per second. The conversion between a frequency f measured in hertz and an angular velocity ω measured in radians per second are:

$\omega = 2\pi f \,$ and $f = \frac{\omega}{2\pi} \,$ .

This SI unit is named after Heinrich Hertz. As with every International System of Units (SI) unit whose name is derived from the proper name of a person, the first letter of its symbol is upper case (Hz). When an SI unit is spelled out in English, it should always begin with a lower case letter (hertz), except where any word would be capitalized, such as at the beginning of a sentence or in capitalized material such as a title. Note that "degree Celsius" conforms to this rule because the "d" is lowercase. —Based on The International System of Units, section 5.2.

History

The hertz is named after the German physicist Heinrich Hertz (1857–1894), who made important scientific contributions to the study of electromagnetism. The name was established by the International Electrotechnical Commission (IEC) in 1930.^[6] It was adopted by the General Conference on Weights and Measures (CGPM) (Conférence générale des poids et mesures) in 1960, replacing the previous name for the unit, cycles per second (cps), along with its related multiples, primarily kilocycles per second (kc/s) and megacycles per second (Mc/s), and occasionally kilomegacycles per second (kMc/s). The term cycles per second was largely replaced by hertz by the 1970s.

The term "gigahertz", most commonly used in computer processor clock rates and radio frequency (RF) applications, can be pronounced either /ˈɡɪɡəhɜrts/, with a hard /ɡ/ sound, or /ˈdʒɪɡəhɜrts/, with a soft /dʒ/^[7] (see giga-#Pronunciation). The prefix "giga-" is derived directly from the Greek "γιγας" ("giant").

Applications

Sine waves of different frequency.

Details of a heartbeat as an example of a non-sinusoidal periodic phenomenon that can be described in terms of hertz. Two complete cycles are illustrated.

Vibration

A440 Play (help·info).

Sound is a traveling longitudinal wave which is an oscillation of pressure. Humans perceive frequency of sound waves as pitch. Each musical note corresponds to a particular frequency which can be measured in hertz. An infant's ear is able to perceive frequencies ranging from 20 Hz to 20,000 Hz; the average adult human can hear sounds between 20 Hz and 16,000 Hz.^[8] The range of ultrasound, high-intensity infrasound and other physical vibrations such as molecular vibrations extends into the megahertz range and well beyond.

Electromagnetic radiation

Electromagnetic radiation is often described by its frequency—the number of oscillations of the perpendicular electric and magnetic fields per second—expressed in hertz.

Radio frequency radiation is usually measured in kilohertz (kHz), megahertz (MHz), or gigahertz (GHz). Light is electromagnetic radiation that is even higher in frequency, and has frequencies in the range of tens (infrared) to thousands (ultraviolet) of terahertz. Electromagnetic radiation with frequencies in the low terahertz range, (intermediate between those of the highest normally usable radio frequencies and long-wave infrared light), is often called terahertz radiation. Even higher frequencies exist, such as that of gamma rays, which can be measured in exahertz. (For historical reasons, the frequencies of light and higher frequency electromagnetic radiation are more commonly specified in terms of their wavelengths or photon energies: for a more detailed treatment of this and the above frequency ranges, see electromagnetic spectrum.)

Computing

In computing, most central processing units (CPU) are labeled in terms of their clock rate expressed in megahertz or gigahertz (10⁶ or 10⁹ hertz, respectively). This number refers to the frequency of the CPU's master clock signal ("clock rate"). This signal is simply an electrical voltage which changes from low to high and back again at regular intervals. This signal is a square wave. Hertz has become the primary unit of measurement accepted by the general populace to determine the performance of a CPU, but many experts have criticized this approach, which they claim is an easily manipulable benchmark.^[9] For home-based personal computers, the CPU has ranged from approximately 1 megahertz in the late 1970s (Atari, Commodore, Apple computers) to up to 6 GHz in the present (IBM POWER processors) and up to 8 GHz overclocked (AMD FX processors).^[10]

Various computer buses, such as the front-side bus connecting the CPU and northbridge, also operate at different frequencies in the megahertz range

SI multiples

SI multiples for hertz (Hz)
Value	Symbol	Name	Value	Symbol	Name
Submultiples			Multiples
10⁻¹ Hz	dHz	decihertz	10¹ Hz	daHz	decahertz
10⁻² Hz	cHz	centihertz	10² Hz	hHz	hectohertz
10⁻³ Hz	mHz	millihertz	10³ Hz	kHz	kilohertz
10⁻⁶ Hz	µHz	microhertz	10⁶ Hz	MHz	megahertz
10⁻⁹ Hz	nHz	nanohertz	10⁹ Hz	GHz	gigahertz
10⁻¹² Hz	pHz	picohertz	10¹² Hz	THz	terahertz
10⁻¹⁵ Hz	fHz	femtohertz	10¹⁵ Hz	PHz	petahertz
10⁻¹⁸ Hz	aHz	attohertz	10¹⁸ Hz	EHz	exahertz
10⁻²¹ Hz	zHz	zeptohertz	10²¹ Hz	ZHz	zettahertz
10⁻²⁴ Hz	yHz	yoctohertz	10²⁴ Hz	YHz	yottahertz
Common prefixed units are in bold face.

Frequencies not expressed in hertz

Even higher frequencies are believed to occur naturally, in the frequencies of the quantum-mechanical wave functions of high-energy (or, equivalently, massive) particles, although these are not directly observable, and must be inferred from their interactions with other phenomena. For practical reasons, these are typically not expressed in hertz, but in terms of the equivalent quantum energy, which is proportional to the frequency by the factor of Planck's constant.

References

^ "hertz". (1992). American Heritage Dictionary of the English Language, 3rd ed. Boston: Houghton Mifflin.
^ "SI brochure: Table 3. Coherent derived units in the SI with special names and symbols". http://www.bipm.org/en/si/si_brochure/chapter2/2-1/second.html. Retrieved 20102025.
^ "[Resolutions of the CIPM, 1964 - Atomic and molecular frequency standards"]. SI brochure, Appendix 1. http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf. Retrieved 2010-20-26.
^ NIST Guide to SI Units - 9 Rules and Style Conventions for Spelling Unit Names, National Institute of Standards and Technology
^ "SI brochure, Section 2.2.2, paragraph 6". http://www.bipm.org/en/si/derived_units/2-2-2.html.
^ "IEC History". Iec.ch. 1904-09-15. http://www.iec.ch/about/history/overview/. Retrieved 2012-04-28.
^ "Gigahertz" in Dictionary.com Unabridged. Dictionary.
^ Ernst Terhardt (2000-02-20). "Dominant spectral region". Mmk.e-technik.tu-muenchen.de. http://www.mmk.e-technik.tu-muenchen.de/persons/ter/top/dominant.html. Retrieved 2012-04-28.
^ Amit Asaravala (2004-03-30). "Good Riddance, Gigahertz". Wired.com. http://www.wired.com/news/business/0,1367,62851,00.html. Retrieved 2012-04-28.
^ By RMorin on Sep 23, 2011. "AMD Breaks 8GHz Overclock with Upcoming FX Processor, Sets World Record". HotHardware. http://hothardware.com/News/AMD-Breaks-Frequency-Record-with-Upcoming-FX-Processor/. Retrieved 2012-04-28.

External links

BIPM Cesium ion f_Cs definition
National Research Council of Canada: Generation of the Hz
National Research Council of Canada: Cesium fountain clock
National Physical Laboratory: Trapped ion optical frequency standards
National Research Council of Canada: Optical frequency standard based on a single trapped ion
National Research Council of Canada: Optical frequency comb
One Hertz in Radians per Second (Google). Note, as of 06 May 2009 there is an error of 2.

UpToDate Contents

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1. 痙攣発作およびてんかんの診断における脳波検査（EEG） electroencephalography eeg in the diagnosis of seizures and epilepsy
2. 非虚血性心疾患および心臓移植における加算平均心電図の利用 use of the signal averaged electrocardiogram in nonischemic heart disease and cardiac transplantation
3. 正常な睡眠の段階および構造 stages and architecture of normal sleep
4. 小児における聴覚障害の評価 evaluation of hearing impairment in children
5. 臨床神経生理学 clinical neurophysiology

English Journal

Synergistic antinociceptive effects of N-methyl-D-aspartate receptor antagonist and electroacupuncture in the complete Freund's adjuvant-induced pain model.

Jang JE, Kim HE, Koo SA, Shin HY, Choe ES, Choi BT.SourceDivision of Meridian and Structural Medicine, School of Korean Medicine, Pusan National University, Yangsan 626-870, Republic of Korea.
International journal of molecular medicine.Int J Mol Med.2011 Oct;28(4):669-675. doi: 10.3892/ijmm.2011.728. Epub 2011 Jun 17.
This study examined the synergistic antinociceptive effects associated with signaling pathway proteins of the spinal cord in a complete Freund's adjuvant (CFA)-induced pain model when electroacupuncture (EA) and a N-methyl-D-aspartate receptor (NMDAR) antagonist were administered in combination. EA
PMID 21687934

The effect of cyclic hydrostatic pressure on the functional development of cartilaginous tissues engineered using bone marrow derived mesenchymal stem cells.

Meyer EG, Buckley CT, Steward AJ, Kelly DJ.AbstractMechanical signals can play a key role in regulating the chondrogenic differentiation of mesenchymal stem cells (MSCs). The objective of this study was to determine if the long-term application of cyclic hydrostatic pressure could be used to improve the functional properties of cartilaginous tissues engineered using bone marrow derived MSCs. MSCs were isolated from the femora of two porcine donors, expanded separately under identical conditions, and then suspended in cylindrical agarose hydrogels. Constructs from both donors were maintained in a chemically defined media supplemented with TGF-β3 for 42 days. TGF-β3 was removed from a subset of constructs from day 21 to 42. Loaded groups were subjected to 10 MPa of cyclic hydrostatic pressurisation at 1 Hz for one hour/day, five days/week. Loading consisted either of continuous hydrostatic pressure (CHP) initiated at day 0, or delayed hydrostatic pressure (DHP) initiated at day 21. Free swelling (FS) constructs were cultured in parallel as controls. Constructs were assessed at days 0, 21 and 42. MSCs isolated from both donors were morphologically similar, demonstrated comparable colony forming unit-fibroblast (CFU-F) numbers, and accumulated near identical levels of collagen and GAG following 42 days of free swelling culture. Somewhat unexpectedly the two donors displayed a differential response to hydrostatic pressure. For one donor the application of CHP resulted in increased collagen and GAG accumulation by day 42, resulting in an increased dynamic modulus compared to FS controls. In contrast, CHP had no effect on matrix accumulation for the other donor. The application of DHP had no effect on either matrix accumulation or construct mechanical properties for both donors. Variability in the response to hydrostatic pressure was also observed for three further donors. In conclusion, this study demonstrates that the application of long-term hydrostatic pressure can be used to improve the functional properties of cartilaginous tissues engineered using bone marrow derived MSCs by enhancing collagen and GAG accumulation. The response to such loading however is donor dependent, which has implications for the clinical utilisation of such a stimulus when engineering cartilaginous grafts using autologous MSCs.
Journal of the mechanical behavior of biomedical materials.J Mech Behav Biomed Mater.2011 Oct;4(7):1257-65. Epub 2011 Apr 22.
Mechanical signals can play a key role in regulating the chondrogenic differentiation of mesenchymal stem cells (MSCs). The objective of this study was to determine if the long-term application of cyclic hydrostatic pressure could be used to improve the functional properties of cartilaginous tissues
PMID 21783134

Japanese Journal

Assessment and follow-up of intercostal nerve damage after video-assisted thoracic surgery.

Miyazaki Takuro,Sakai Tetsuya,Tsuchiya Tomoshi,Yamasaki Naoya,Tagawa Tsutomu,Mine Mariko,Shibata Yoshisada,Nagayasu Takeshi
European journal of cardio-thoracic surgery : official journal of the European Association for Cardio-thoracic Surgery 39(6), 1033-1039, 2011-06
… Intercostal nerve function was assessed by a series of 2000-Hz (Aβ fiber), 250-Hz (Aδ fiber), and 5-Hz (C fiber) stimuli using current perception threshold testing (Neurometer CPT/C(®)). …
NAID 120002709179

Li およびK 形陽イオン交換樹脂 / 純水系のインピーダンス測定

岩元和敏,黒田雄大
東海大学紀要. 開発工学部 20, 157-161, 2011-03-31
… 充填し,高純度水を循環させながらインピーダンス測定を行った.加える交流の実効電圧を一定に保ち,周波数を1 MHz から20 Hz へ変えながらインピーダンスを測定し,複素平面上に図示したところ,各イオンとも高周波数領域で傾き45°の直線になることが示された.さらに周波数が60 Hz くらいまで低下すると,Na 形およびK 形陽イオン交換樹脂の場合は,45°より大きな傾きをもつ第二の直線上に不連続に移動 …
NAID 110008148670