Doppler shift

Doppler effect is a memorial to Christian Johann Doppler, named after the, he in 1842 firstly put forward this theory. Main contents: the wavelength of the light source object radiation because the observer and the relative motion changes. In the movement of the waves, wave front compressed, wavelength becomes shorter, frequency becomes higher (blueshift blue shift); When moving in waves behind, can produce adverse effect. Wavelength becomes longer, frequency become low (redshift ep-red shift). The higher the speed of the waves, the effects of refuse. According to the light red (blue) move degree, can calculate waves followed the observation direction movement speed

The cause

1842 Austria named doppler mathematician and physicist. One day, he was passing by railway crossing zero at a train from his side est, he found the train from far and close the whistle variable ring, tones, but the train variable pointed from far and near when the whistle slacken, tone become low. He knew the physical phenomenon felt great interest, and studied. Find this is due to vibration sources and observers exists between the relative motion, make the observer audible voice frequency different YuZhenYuan frequency phenomenon. This is frequency shift. Because, sound relative to the observer is moving, observers have heard the voices will change. When sound from the observer, acoustic wavelength increases, tones descended, when sound sources close to the observer, acoustic wavelength decreases, and tone become tall. With sound and tones of change of the relative speed between the observer and sound velocity ratio of relevant. This ratio is larger, the more significant change, the posterity is called it "the doppler effect".

The acoustic as regular interval emitted pulses can imagine if you each step, they launched a pulse, so before you each pulse is bigger than you stood motionless when closer to you. And behind you sound is than the original fixed when far step. Or, before you become the pulse frequency than usual after you high, while the pulse frequency are lower than usual.

So-called doppler effect is when its source and receiving body exists between the relative motion, receiving body receives its source emission information frequency and its source launch the frequency of information are not identical, this phenomenon is called doppler effect, receive frequency and transmit frequency difference is called the doppler frequency. The spread of voice also exist doppler effect, when the source and receiving between body have relative motion, receiving body receiving acoustic frequency f 'and noise resource frequency f exist doppler frequency shift Δ f (doppler shift) namely

Δ f = f '- f

When receiving body and sound near each other, receive frequency f 'greater than the transmit frequency f namely

Δ f > 0

When receiving body and sound going away from each other, receive frequency f 'less than transmit frequency namely:

Δ f < 0

Can proof if receiving body and sound near each other or going away from each other for v, the speed of sound velocity for c, then receive body receiving sound wave doppler frequency for:

F '= f. (v) / c + + v) (c -

Parentheses molecules and denominator upline operations and descending computing respectively to "close" and "from" meaning.

Application examples

Doppler effect not only applicable to sound waves, it also apply to all types of wave, including wavelengths. Edwin Hubble scientists using doppler effect that the universe is expanding conclusion. He found that distant galactic light frequency in become low, namely to move to the red end of the spectrum. This is red the doppler frequency, or called redshift. If the galaxy is moving towards the blue end, the light will become blue shift.

In mobile satellite communications, when the plane moving towards the satellite, frequency becomes tall, far from satellite, frequency become low, and because of the speed of an airplane is very quickly, so we in mobile satellite communications should be fully considered "dopplereffect". On the other hand, because the geosynchronous satellites itself also have high speed, so now mainly use geosynchronous satellites and airplanes to communicate, and to avoid this kind of influence and cause us problems in communication, we have to be different considerations in technology. Also increases the complexity of mobile satellite communication.

Sound wave doppler effect also can be used in medical diagnosis, namely we ordinary sufficiency. Color dopplar ultrasound simply means high definition of black and white b-sonography plus color doppler, first say super audio move diagnostics, namely D super, in this application doppler effect principle, when the source and receiving body (namely probe and reflector) between the relative motion, the echo of frequency changing, this frequency changes called doppler-shift, D super including pulsed doppler, continuous doppler and color doppler images. Color doppler ultrasound is commonly use the relevant technology doppler signal processing, the autocorrelation technology for blood signal by color coding after real-time overlay on 2-d image, it forms of color doppler ultrasound image blood flow. Thus, color doppler ultrasound (i.e. color dopplar ultrasound) has both the advantages of structure of two-dimensional ultrasound images, and also provides hemodynamic of the rich information, practical applications received wide attention and welcome, in clinical is known as "nontraumatic angiography". 

Full-duplex

Full-duplex communication transmission is a term

At the same time transitions is only allowed either party may transmit information, and other one party cannot transmit to party

Full-duplex is in microprocessor and peripheral equipment by sending line between independent and accept line method, can make the data in both directions simultaneously transmit operation. To send data refers in the also able to receive data, both synchronously, it seems we usually call is same, also can hear speaking the voice on the other. The current nic generally support full-duplex.

Half-duplex, so-called half-duplex refers to a period only an action happens, give a simple example, a narrow road, also can have a car through, when there are two car folio volume at present, this kind of circumstance can only a car first, wait until after the other one head again, this example is the description of the image of half-duplex principle. Early interphone, as well as early hubs etc equipment are based on half-duplex products. As technology advances, half double union gradually withdraw from the stage of history.

Full-duplex Ethernet use two cables, rather like the half-duplex mode that USES a pair of cable. Full-duplex mode in sending equipment of the sender and the receiver between the receiving device adopt point-to-point connections, this means that in full-duplex transmission mode, can get higher data transfer rate. 

Cycling exercise can prolong life

The bike is a common and convenient traffic tools, but also a good sport. Along with the people environmental protection and fitness awareness enhancement, choose bikes and exercise, by many people praise highly.

Cycling travel into English the rich new fashion

"Poor cycling crowded Mr, the rich driving sit big rush." Traffic tools, seems to have been the important people to identify the identity characteristics. But according to Britain's daily mail reported recently, the British ministry of a nationwide travel survey, British people more rich, he rode bicycles mileage is longer. Survey found with Britain's poorest one fifth of the country's population, compared the richest one fifth of the population, an average annual bike travel distance length is former 5 times.

British bicycle promotion organization "riding England" controller introduces, all British bicycle has sold from 2000 of the 280 million vehicles increased by 2006, 3.5 million vehicles, London number of cycling since 2000 already rose 83%.

"Ride travel is becoming a fashion. British "London cycling" spokesman said, "open car show everywhere, prove himself social status of age has in the past, a bicycle life just more cool." And cycling travel to exercise, let a person more healthy, also can protect the environment, reduce the air pollution and noise pollution. In Britain, choose this green travel mode has become a people who have received higher education, has the sense of responsibility, being also confident performance.

Cycling exercise prolong life

Britain recently a study also indicate that cyclists health than their younger equivalent to ten years old, while people who came to more than 30 years old still insist on regular riding person, can make own life expectancy rose by an average of 2 years.

Beijing sport university sports medicine research of human movement academy of sciences, said professor LiuYi sails cycling and running, swimming is same, it is a kind of can improve people cardiorespiratory function endurance sex exercise. It not only can exercise the muscle joints, reduce weight, symmetrical figure, but can also strengthens the heart, prevent hypertension, also can rise to prevent the aging brain, improve the nervous system agility role. "Bicycle ergometer make the blood circulation acceleration, allow the brain to consume more oxygen, keep clear thinking."

Cycling exercise "three note"

"Bicycle sport to body many benefits, but there are also many precautions." LiuYi sails said, first of all, to grasp the time well, general each cycling time should be controlled in 30-60 minutes, speed can according to each physique to adjust, but unfavorable too fast vastly. Secondly, by bicycle, we must keep the correct posture, adjust the height of his hands and bicycle saddles, Trample baseboard, foot position to appropriate, forcibly even, note a rhythm, otherwise, it will make ankle and knee pain occurs. In addition, some with the male reproductive system diseases, epilepsy patients, serious heart disease patients and in physiology cycle of female, not suitable for long time cycling exercises.

With the city highway environmental pollution bigger, automobile exhaust gas and dust in the movement of people to produce very big damage, therefore, LiuYi sails Suggestions, ride a bike travel to try to avoid the severe pollution of the street, but choose environment better route. "Those working place far away, it is not convenient to bike riding person, also can choose indoor fixed bicycle to exercise." 

Winter to eat meat can cure diseases fitness

Mutton to eat large, steaming, boiling, frying, rinse, and so are all available. Winter is the best season to eat mutton tonic, if combined with certain drugs will be made of lamb diets, the greater curative powers Fitness
Mutton 150 grams, 100 grams of rice, ginger 5. A total of porridge, oil, salt to taste. Physically weak governance cold, backache Tuiruan, kidney impotence, nocturnal emission, premature ejaculation, menstrual disorders, deficiency of blood through the pain.
250 grams of lamb, pig 1, with the soup, add a little salt and spices. 2 times the solar eclipse, and even food for 1 week. Attending post-natal no milk and less milk.
1,000 grams of meat, licorice, angelica 10 grams, salt, ginger, cinnamon, star anise and adequate water, cook a small fire. Both on a good winter tonic, but also governance old cold, cold cough, physically weak cold, backache petrified, frequent urination.
500 grams of lamb, Astragalus, Codonopsis, 30 grams, 25 grams of ginger, angelica 20 grams cook. Meat soup, blood weak governance, malnutrition, anemia, fever, sweating, cold limbs.
250 grams of mutton, boiled, together with 500 grams of fresh yam, rice 250 grams, Zhu Chengyu. Sooner or later eat 1, cure loss of appetite, loose stool, backache, frequent urination, weak and chills.
200 grams of lamb, angelica 15 grams, ginger 30 grams, 10 grams of light blue, Gong Zhu, add salt and other spices, meat soup, governance virtual cold nausea, Han Shan, and cold.
Mutton, ginger, cinnamon, Kou Yan, fennel and other spices. Slice cooked food, cure spleen Deficiency caused the indigestion, abdominal pain, lassitude Leng Tong.
Lamb with dried shrimp, ginger, green onions for soup, to kidney.
Lamb Astragalus, swim bladder, Shuijianbi, cure enuresis, urinary frequency.
Mutton smell great, 1,000 grams of meat plus 10 grams of licorice, wine, ginger amount of boiling about its smell can be removed.
Note: The lamb bogey bronze, anti-Breit, iris, and is not with the pumpkin with the food.

Omnidirectional Antenna

Omnidirectional antenna, that is, the performance graph in the horizontal direction is 360 ° are uniform radiation, which is usually referred to no direction, the performance graph in the vertical direction to have a certain width of the beam, in general, the smaller the beam width, Gain greater. Omnidirectional antenna in mobile communication systems and the general application of the system of suburban stations Region-based, large coverage area.

Dual Stack

Dual-stack node using the technology to run IPv4 and IPv6 protocol stack sets. This is the IPv6 nodes to maintain compatibility with the pure IPv4 node most direct way to communicate targeted at end nodes (including hosts, routers). IPv4 and IPv6 in this way provides a fully compatible, but for the IP address depletion problem is not any help. Due to the need dual-route infrastructure, this approach actually increased the complexity of the network.
 First, the dual-stack work Dual Stack refers to a single node to support both IPv4 and IPv6 protocol stacks of two. IPv6 and IPv4 is the function of the network layer protocol similar, both are based on the same physical platform and its load on the transport layer protocol TCP and UDP are basically no difference, therefore, support both dual-stack node and IPv4 node communication protocol support, but also with the support of IPv6 protocol nodes. It is believed that the network all the major service providers in the network before the upgrade to IPv6, will support dual-stack operation. 1. Receives the packet Dual-stack node and other types of multi-stack nodes work the same way. Link layer data segment is received, open and check the header. IPv4/IPv6 header if the first field, the IP packet version number is 4, the packet to the IPv4 stack to deal with; If the version number is 6, by the IPv6 stack processing; If the establishment of an automatic tunneling mechanism, the use of appropriate technology will be re-integrated into IPv6 packets of data packets handled by the IPv6 stack. 2. Send data packets As dual-stack IPv4 and IPv6 host support both two kinds of agreements, so when its time to communicate in the network needs to determine the circumstances in which a protocol stack used for communication, which need to develop dual-stack work. In the network communication process, the destination address as the main parameters of the routing, so depending on the application procedures used by the destination address of the protocol type of the dual-stack work to make the following conventions: (1) If the application uses the destination address for the IPv4 address, IPv4 protocol is used; Suppose node A and node B communications, A for the dual stack node, node B supports IPv4 protocol (the destination address for the IPv4 address). A dual stack node will work: Node B using the IPv4 communication protocol. Completeness: Node A has two options, the use of IPv4 or IPv6 protocol agreement with the host B communicate. Under the given conditions, A, B nodes are supported IPv4 protocol, so I chose to IPv4 protocol can guarantee the normal communication, it is agreed upon is sufficient. If you use the IPv6 protocol for communication, because we can not determine whether the dual stack node B (for a given condition is just the destination address for the IPv4 address), so when the node B does not support the IPv6 protocol can not guarantee the normal communication, it is agreed is necessary. At this point that the convention (1) is complete. (2) If the destination address for the IPv6 address, and for the local online network, use the IPv6 protocol. (3) If the application uses the destination address for the IPv4-compatible IPv6 addresses, and non-local online network, use the IPv4 protocol, IPv6 will be at this time In encapsulated in IPv4. IPv4-compatible IPv6 address, IPv6 protocol specification is provided in a special address. Such addresses are 0, high 96, low 32 bits contain IPv4 addresses. IPv4-compatible address is the node for the router to tunnel through the transmission of IPv4 IPv6 packets, the nodes to understand both IPv4 and understanding of IPv6. Can automatically tunnel IPv6 packets in IPv4 network mode IPv4/IPv6 dual stack node transmission will use these addresses. IPv6 address specifications under the agreement, and (3) the assumed conditions, can determine the destination node B is also a dual stack node, and IPv4/IPv6 transition period with the basic situation of the network, node A and node B will be across the IPv4 network communication, so using the IPv4 protocol is feasible. Of course, you can also communicate using the IPv6 protocol, but in the early transition years, (3) the agreement will be superior to using the IPv6 protocol. (4) If the application uses the destination address is non-compatible IPv6 address IPv4, non-local online network, use the IPv6 protocol. Similar to the convention (2), using the IPv6 protocol can guarantee the normal communication, and if it is pure IPv4 network across the communication mechanisms such as the use of the tunnel for communication; and if the local network, the tunnel mechanism is not required to complete the communication. (5) If the application uses the domain name as the destination address, domain name server to start the corresponding IPv4/IPv6 address, then address the appropriate handling of the situation. Above (1) to (5) is the dual-stack work, with the constant expansion of IPv6 network, these methods will do the appropriate changes and additions, which will depend on the transition process and IPv6 networks continue to evolve . Second, based on dual-stack applications 1. Based on dual-stack domain name service domain name system (referred to as: DNS) The main function of the domain name and IP address through the interaction between the corresponding relationship to precisely locate network resources that, according to domain name queries IP addresses, and vice versa. DNS is the Internet's infrastructure, many network services are built based on the DNS system. Therefore, DNS importance of self-evident. IPv4 address of a positive resolution of the resource record is "A" record. There are two kinds of IPv6 address resolution resource records, that is, "AAAA" and "A6" records. "A6" record to support a number of "AAAA" do not have new features, such as address aggregation, change of address (Renumber) and so on. Exist in the DNS server "A" record and "AAAA" (or "A6") records. Since the node can handle both IPv4 protocol, IPv6 protocol can handle, so no DNS ALG and other switching equipment. DNS server to answer either "A" record or "AAAA" records, can communicate. 2. Based BBS services, dual-stack BBS is a communication platform on the Internet, the Web services play an important role, along with the smooth transition of IPv4 to IPv6, created based on dual-stack BBS service system becomes necessary. According to the "basic support for IPv6, socket (socket) interface expansion", modify the relevant parts of the code, you can achieve IPv6 and IPv4-compatible BBS system.
 (1) IPv6 socket address structure Defined in <sys/socket.h> IPv6 --- AF_INET6 address family and protocol family --- PF_INET6, or the new sockaddr_in6 data structure sockaddr_in data structure with the original distinction, which will create the socket when use. (2) IPv6 address several specific structures to support IPv6, BBS systems, use the following two special IPv6 addresses. ① IPv4 addresses mapped IPv6 address. ② IPv6 wildcard address.
 (3) How to make the program compatible with IPv4/IPv6 most of the existing IPv4 network application is written, the principle can be seen from the above, except for some closely related with the characteristics of IPv4 procedures (such as the use of multicasting, IP options or the original set of interface programs), most of the application to convert IPv4 IPv4/IPv6 application compatibility is not very difficult. Based on this idea, according to the IPv4 and IPv6 Socket API made compatible with the support of the existing BBS system (IPv4-based application system) a series of changes to support IPv6, to construct a BBS system. Take the following major steps: ① to construct a dual stack (Dual Stack) BBS server, IPv4 and IPv6 addresses were given, making its services running on the BBS handle both IPv4 clients use, capable of handling the use of IPv6 customers.
 ② IPv4 socket address of the original part of the modification, creation based on IPv6 sockets.
 ③ IPv6 socket will be bound to the IPv6 wildcard address and listening port 23.
 ④ The transfer function compatible with IPv4/IPv6 addresses instead of IPv4-only support address translation function. ⑤ to amend the IP address displayed in the format of the relevant code, with sufficient length Show support for IPv6 addresses. 3. IPv6 Campus Transition Plan During the transition process, IPv6 IPv4 access network segment as the islands, and between network segments to achieve IPv6 IPv4, IPv6 interoperability between network segments, a variety of transitional technologies must be integrated to optimize network structure, network security and reliable operation, and a gradual transition, saving investment under the premise of the transition program design. Based on the above basic principles, and network operating conditions, for the early stages of the transition program of Campus Network Planning are as follows: (1) cross-communication between IPv4 network using IPv6 tunneling technology; (2) server based on the escalation of IPv4 to dual stack node server; (3) IPv4/IPv6 interoperability client can use NAT-PT technology; (4) The export of local IPv6 router access to higher segment associated IPv6 network. In carrying out the early stages of IPv6 applications should try to ensure the existing network system safe and stable operation, so for the new IPv6 network segments, should be independent of access to higher link IPv6 network. Select dual-stack IPv6 router segment as the access node, to ensure that the new IPv6 network segment can also use the local network services.

Diving light equipment Sambo

Light equipment refers to the mask, snorkel and fins - Dive Sambo, when you have these pieces of snorkeling equipment on it, and scuba diving are also needed heavy equipment, referring to the buoyancy adjustment device (BC ), breathing regulator, scuba diving instruments, gas cylinders and so on. There are numerous diving equipment styles and colors, you can dive in the form, purpose, their own preferences and physical characteristics to select the different characteristics of the equipment.
Mirror - window to the underwater world
Try to open my eyes in the water, could see only a blur in the picture, it is because the density of water than air, the light will be refracted into the water. The focal length of the eye is based on the light to adjust the air, so keep your eyes mirror to the cavity, so that you have a clear line of sight. Mask and swimming goggles biggest difference is that the former is not only the nose covered with eyes still covered, because the dive in order to prevent extrusion, the need to balance the pressure within the nasal cavity, so the swimming goggles can not be used for diving.
Generally mirror the enhanced safety glass lenses, fitting face of the rubber or silicone base side and adjust the headband can be composed of a fixed position. Enhanced safety glass lens to prevent the risk of breaking into a highly elongated glass. Group is stronger than silicone rubber side of the material, it is because silicone rubber durable than 3-4 times, not easy to skin allergies, more soft and comfortable. Some mirror has a drain valve is a one-way valve mask is used to eliminate the water. Choose mirror of the most important points is appropriate and comfortable or not, other equipment as well. A mirror may be inappropriate leakage may also cause allergies and reduce a lot of fun diving.
Test mask fit or not, as long as the mask gently to your face (do not take headband) and then use the nose and the right mirror will close in the face until you exhale. Another point to note is, make sure you can easily pinch your nose in the mirror outside. A variety of mask styles, with single lenses, two lenses and a variety of multi-piece lenses, the lens is usually only two models available with corrective lenses.
The first time in the mirror can be used before using a soft cloth lightly moistened wipe toothpaste on both sides of the lens to remove the protective film. Mirror is required after each use with water to fully clean, placed in a dry and ventilated place, not exposed to direct sunlight. If you are using a mirror in the water, preferably warm water for a few minutes can be used to prevent corrosive salt scale production. If you can not wash immediately after use, preferably the mirror on the water, because the kill is difficult to completely remove the salt.
Breathing tube - breathe easily
You might think that since there is scuba diving cylinder and regulator, why one of the breathing tube is also standard equipment? Because first of all, when your water breaks or swimming, your face is looking down in the water or find something , you can breathe through the breathing tube in order to reduce the consumption of air cylinders. Second, when the water is rough, you can use breathing tube nozzle height is usually higher than the wave height and avoid the water poured into the mouth. Third, if you are away from the vessel or the shore water, and gas cylinders in the air was running low, breathing tubes more easily make your trip back to the boat or shore, your face on the water can be naturally . In the snorkeling, the breathing tube is necessary equipment, you can not stay on the rise in the water all day. Try it.
Breathing tube design is generally open at one end the other end there is a mouthpiece of the pipe. The upper breathing tubes (the tube body) is usually semi-rigid plastic tube, the bottom half of more than the silicone mouthpiece. A suitable curvature of the breathing tube should be appropriate (for your own face), about 2 cm diameter, length 30 to 35 cm. In addition to comfortable right outside the breathing tube still breathing easy. Trial, can be put mouthpiece between lips and teeth, against the left ear before the tube body, mouthpiece should fit comfortably and will not scratch the mouth or chin, caused by fatigue, and that is straight in her mouth The.
Webbed feet - provides a powerful forward momentum
Webbed feet wide area can provide you with a powerful driving force, so that you do not have to rely on paddling his hands to generate power, so both hands can be freed for other work. Webbed feet are divided into free now, and two sets of feet. Sets foot fins are generally used for warm waters, or snorkeling. No Genjiao fin used with the diving boots. Large and hard to use, fast and webbed feet, but the fatigue and cramping; small and soft, the lack of driving force fins.
Fins with different materials, design and features. Webbed feet design include: the keel, used to increase the hardness and balance fins; drainage holes to reduce the resistance of the fins to increase efficiency; diversion ditch, so that the level of slip over the fins to increase the speed. Select flippers according to your body, physical and diving environment, it is important comfortable and appropriate.