Wednesday, December 2, 2009

Inverse square law

Inverse-square law
From Wikipedia, the free encyclopedia
(Redirected from Inverse square law)


Light and other electromagnetic radiation

This article may need to be wikified to meet Wikipedia's quality standards. Please help by adding relevant internal links, or by improving the article's layout. (October 2009)
The intensity (or illuminance or irradiance) of light or other linear waves radiating from a point source (energy per unit of area perpendicular to the source) is inversely proportional to the square of the distance from the source; so an object (of the same size) twice as far away, receives only one-quarter the energy (in the same time period).
More generally, the irradiance, i.e., the intensity (or power per unit area in the direction of propagation), of a spherical wavefront varies inversely with the square of the distance from the source (assuming there are no losses caused by absorption or scattering).
For example, the intensity of radiation from the Sun is 9140 watts per square meter at the distance of Mercury (0.387AU); but only 1370 watts per square meter at the distance of Earth (1AU)—a threefold increase in distance results in a ninefold decrease in intensity of radiation.
Photographers and theatrical lighting professionals use the inverse-square law to determine optimal location of the light source for proper illumination of the subject. The inverse-square law can be used only on point source light; a fluorescent lamp is not a point source and therefore one can not use the inverse-square law, as is possible with most other light sources, with a fluorescent lamp.







The lines represent the flux emanating from the source. The total number of flux lines depends on the strength of the source and is constant with increasing distance. A greater density of flux lines (lines per unit area) means a stronger field. The density of flux lines is inversely proportional to the square of the distance from the source because the surface area of a sphere increases with the square of the radius. Thus the strength of the field is inversely proportional to the square of the distance from the source.
In physics, an inverse-square law is any physical law stating that some physical quantity or strength is inversely proportional to the square of the distance from the source of that physical quantity.
Contents [hide]
1 Justification
2 Occurrences
2.1 Gravitation
2.2 Electrostatics
2.3 Light and other electromagnetic radiation
2.3.1 Example
2.4 Acoustics
2.4.1 Example
3 Field theory interpretation
4 See also
5 External links
6 Notes
[edit]Justification

The inverse-square law generally applies when some force, energy, or other conserved quantity is radiated outward radially from a source. Since the surface area of a sphere (which is 4πr 2) is proportional to the square of the radius, as the emitted radiation gets farther from the source, it must spread out over an area that is proportional to the square of the distance from the source. Hence, the radiation passing through any unit area is inversely proportional to the square of the distance from the source.
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Wednesday, April 29, 2009

Volatile memory

Volatile memory

From Wikipedia, the free encyclopedia

Computer memory types
Volatile
Non-volatile

Volatile memory, also known as volatile storage or primary storage device, is computer memory that requires power to maintain the stored information, unlike non-volatile memory which does not require a maintained power supply.

Most forms of modern random access memory (RAM) are volatile storage, including dynamic random access memory (DRAM) and static random access memory(SRAM). Content addressable memory and dual-ported RAM are usually implemented using volatile storage. Early volatile storage technologies include delay line memory and Williams tube.
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Sunday, April 19, 2009

Non-volatile memory

Non-volatile memory

From Wikipedia, the free encyclopedia

Computer memory types
Volatile
Non-volatile

Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory, flash memory, most types of magnetic computer storage devices (e.g. hard disks, floppy disks, andmagnetic tape), optical discs, and early computer storage methods such as paper tape and punch cards.

Non-volatile memory is typically used for the task of secondary storage, or long-term persistent storage. The most widely used form of primary storage today is a volatile form of random access memory (RAM), meaning that when the computer is shut down, anything contained in RAM is lost. Unfortunately, most forms of non-volatile memory have limitations that make them unsuitable for use as primary storage. Typically, non-volatile memory either costs more or performs worse than volatile random access memory.

Several companies are working on developing non-volatile memory systems comparable in speed and capacity to volatile RAM. For instance, IBM is currently developingMRAM (Magnetic RAM). Not only would such technology save energy, but it would allow for computers that could be turned on and off almost instantly, bypassing the slow start-up and shutdown sequence.

A number of conferences are held every year that focus specifically on non-volatile memory. One of the most prominent is the Non-Volatile Memory Technology Symposium ([1]).

Non-volatile data storage can be categorised in electrically addressed systems read only memory and mechanically addressed systems hard disks, optical disc,magnetic tape, holographic memory and such. Electrically addressed systems are expensive, but fast, whereas mechanically addressed systems have a low price per bit, but are slow. Non-volatile memory may one day eliminate the need for comparatively slow forms of secondary storage systems, which include hard disks.
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P2 (storage media)

P2 

From Wikipedia, the free encyclopedia

  (Redirected from P2 Card)

P2 (P2 is short form for "Professional Plug-In") is a professional digital video storage media format introduced by Panasonic in 2004, and especially tailored to ENG applications. It features tapeless (non-linear) recording of DVCPRO, DVCPRO50, DVCPRO-HD, or AVC-Intra streams on a solid state flash memory card. The P2 Card is essentially a RAID of SD memory cards with an LSI controller tightly packaged in a die-cast PC card (formerly PCMCIA) enclosure, so data transfer rate increases as memory capacity increases. The system includes cameras, decks as drop-in replacement for VCRs, and a special 5.25" computer drive for random access integration with NLE systems. The cards can also be used directly where a PC card slot is available, as in most notebook computers, as a normal disk drive, although a custom software driver must first be loaded.

As of late 2008, P2 cards are available in capacities of 4, 8, 16, 32GB and 64GB. At introduction, P2 cards offered low recording capacity compared to competing, videotape-based formats (a miniDV tape holds roughly 13GB of data, and an S-size HDCAM tape holds 50GB). To solve this, camcorders and decks using P2 media employ multiple card slots, with the ability to span the recording over all slots. Cards are recorded in sequence, and when a card is full, it can be swapped out while another card is recording. This limits recording time only by power supply and the available amount of cards. If a card is partially full, the deck will record only until it is full. Unlike tape, old video cannot be recorded over accidentally. Old footage must be manually deleted. Since then card capacity has increased to as much as 64GB.

P2 cards are of a ruggedized PCMCIA type with the fastest transfer speeds currently available through this format. The card also contains a processor that organises and safeguards the files and the case is developed and crafted to "military" (according to Panasonic) specifications, making P2 cards tough and reliable.

The first pieces of equipment released by Panasonic which use the P2 format included the AJ-SPX800 (a 2/3" broadcast camcorder for ENG and EFP applictions), the studio recorder AJ-SPD850, the AJ-PCD10 offload device (basically, a five-slot PC card reader with USB interface designed to fit a 5-1/4" IT systems bay), and the memory cards themselves - AJ-P2C004 (4 GB) and AJ-P2C002 (2 GB). Panasonic is currently shipping a wide range of camcorders that support the P2 format, including the professional AG-HVX200 HD handheld camcorder, and the high-end, or broadcast professional shoulder-mount AG-HPX500, AJ-HPX2000, and AJ-HPX3000 camcorders. Panasonic has also announced the P2-based AG-HPX170 handheld HD camcorder. The HPX170 is very similar to the HVX200and the HVX200A, the main difference being the lack of a tape drive on the 170. The latest products to feature P2 technology are the well-received[1] recently launched AJ-HPX2700 and AH-HPX3700 "Varicam" high end cameras.

Contents

 [hide]

[edit]Specifications

  • File format: MXF
  • Maximum datarate: 640 Mbit/s([1])
  • Available sizes: 8 GB, 16GB, 32GB, 64GB
  • Form factor: PC card (PCMCIA) type II

[edit]P2 Workflow

P2 is a solid state technology, and as such departs from the older method of recording video onto tape. Since the video output is saved onto a solid state P2 memory card as a file, many possibilities are opened up to change the approach to workflow; indeed, it is claimed that the workflow can be speeded up and made more reliable, which in turn, reduces production costs [2]. Since its inception, the development of this workflow, together with partners such as Avid and Apple, has matured, and has been adopted by many major production teams. [3]

[edit]P2 Card Run Times Timetable

Model #CapacityDVCProDVCProHD 720pN24DVCPro50 or

DVCProHD 720p30

DVCProHD at

1080i60 or 720p60

AJ-P2C004H4GB16 min.10 min.8 min.4 min.
AJ-P2C008H8GB32 min.20 min.16 min8 min.
AJ-P2C016H16GB1 hr. 4 min.40 min.32 min.16 min
AJ-P2C032H32GB2 hrs. 8 min.1 hr. 20 min.1 hr. 4 min.32 min.

2 GB P2 cards are not supported in DVCProHD applications. There is no release date yet announced for 64GB P2 cards. Panasonic recently published a slightly more complicated version of this table for 16 and 32 GB cards.[4]

[edit]P2 Current Camera Range

[edit]Handheld models

AG-HPX170 (NTSC version)

  • Compact, Lightweight HD/SD Camera-Recorder 



* 13x zoom lens with 28mm wide-angle

AG-HPX171 (European version)

  • Compact, Lightweight HD/SD Camera-Recorder 



*13x zoom lens with 28mm wide-angle 
* Improved ergonomics, features and image quality compared to its predecessor

AG-HVX201

  • Progressive native 16:9 HD 3CCD imaging system
  • HD quality Leica Dicomar wide-angle zoom lens 



* Progressive modes supported

[edit]Shoulder Mount Models

AG-HPX300

  • 3 pieces of 1/3-inch MOS image sensor (1920x1080 pixels each)
  • Removable 1/3-inch lens
  • AVC-Intra 50/100 and DVCPRO HD/50/25 codecs compatible
  • Variable Frame Rate
  • LCoS viewfinder
  • Two P2 slots

AG-HPX301E NEW[5]

  • As above but with many improvements

AG-HPX500

  • 3 pieces of 2/3-inch CCD image sensor (960x540 pixels each)
  • DVCPRO HD/50/25 codecs 
compatible
  • Variable Frame rate function
  • Four P2 slots


AJ-HPX2100 
* 3 pieces of 2/3-inch CCD image sensor (1 million pixels each)

  • DVCPRO HD/50/25 codecs compatible
  • AVC-Intra 50 codec as an option
  • Five P2 slots


AJ-HPX2700

  • One of the new P2 Varicam range
  • Variable Frame Rate of 1 frame/s to 60 frame/s 

  • 10 bit/4:2:2 Recording with Full Sampling 

  • AVC-Intra codec recording system


AJ-HPX3000

  • AVCHD Camcorder


* Native 1080p 4:2:2 10-bit 
* Newly developed high-resolution 2.2-megapixel CCD

  • AVC-Intra codec recording system


AJ-HPX3700

  • High-End HD Camera-Recorder for Cinema Production , part of the P2 Varicam range


* RGB 4:4:4 and 24PsF Output 


  • AVC-Intra codec recording system

[edit]See also

[edit]References

  1. ^ Independent P2 Varicam review
  2. ^ Panasonic Professional User Group Interviews
  3. ^ Panasonic Professional User Group References
  4. ^ Panasonic P2 Panasonic Guidebook
  5. ^ Independent In depth AG-HPX301E review

[edit]External links
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