Doppler Effect and Sonic Booms

DSLR 1.x crop factor vs. Full frame : Effect and reality 1. Crop factor Nếu camera có sensor size nhỏ hơn kích thước bản film chuẩn (24mm x 36mm) thì tỷ lệ nhỏ hơn đó được thể hiện bởi thông số crop factor 1.x . Giả sử APS-C có crop factor là 1.5x, có nghĩa là độ dài đường chéo của sensor ngắn hơn độ dài đường chéo của FF 1.5 lần. 43.27mm : 28.43mm ~ 1.5 lần. 2. Angle view Góc nhìn của một bức ảnh được xác định bởi góc tạo bởi giữa các đỉnh của khuôn hình (hay các đỉnh của sensor) với tâm của hệ thấu kính. (Dpreview) Có 3 loại: Vertical, Horizontal & Diagonal angle view. Và Picture angle of View được lấy theo Diagonal angle of view, tức theo đường chéo của sensor. Như vậy, góc nhìn của ảnh sẽ bị ảnh hưởng bởi hai yếu tố: - Với cùng 1 tiêu cự (lens như nhau) thì angle view sẽ bị ảnh hưởng bởi kích thước sensor: Sensor càng lớn, góc nhin càng rộng và ngược lại. - Với cùng 1 kích thước sensor (body như nhau) thì angle view sẽ bị ảnh hưởng bởi tiêu cự lens sử dụng: Tiêu cự càng dài, góc nhìn càng hẹp và ngược lại. 3. Sensor size, focal length effect Từ những nhận xét trên, đi sâu hơn nữa vào những effect của sensor size và focal length lên một bức ảnh, ta có thể rút ra một số điểm quan trọng sau: - Kích thước sensor chỉ làm giảm (hoặc tăng) góc nhìn của một bức ảnh chứ không hề ảnh hưởng đến kích thước ảnh (subject size) trên sensor. Lý do là tận dụng hệ thống lens 35mm hiện nay thì vị trí của sensor trong các DSLR giống hệt như vị trí của film trong SLR cho nên hình ảnh rơi trên film như thế nào thì cũng rơi trên sensor như vậy. Do đó, kích thước ảnh trên sensor APS-C cũng y hệt kích thước ản rơi trên FF. Tất nhiên, APS-C nhỏ hơn FF nên nó ghi được ít hình ảnh hơn so với FF. Nhưng những gì cả hai cùng ghi được thì đều có kích thước như nhau ! - Việc thay đổi tiêu cự thì lại làm thay đổi cả góc nhìn và kích thước ảnh. Cái này chúng ta đều thấy rõ khi nhìn qua viewfinder kết hợp với zooming. Tiêu cự càng nhỏ (wide angle), góc nhìn càng lớn và kích thước ảnh càng nhỏ, Tiêu cự càng lớn (tele), góc nhìn càng hẹp và kích thước ảnh cảng lớn. Tách riêng ra thì rất rõ ràng như vậy. Nhưng sự "giao thoa" giữa các kích thước sensor khác nhau, với các tiêu cự khác nhau kể từ khi DSLR APS-C ra đời mới nảy sinh nhiều thắc mắc LỢI - HẠI. 4. APS-C , FF with wide angle lens Khi tìm kiếm và sử dụng một wide angle lens, cái tên của nó cũng nói lên chúng ta mong đợi điều gì: Một bức ảnh có góc chụp rộng, thu được nhiều hình ảnh. Không mấy ai quan tâm tới kích thước ảnh. HIển nhiên vì đây cũng k0 phải là tiêu chí của một wide angle lens. Khi đắn đo giữa 12mm và 18mm thì ta quan tâm đến angle view của 12mm thật đáng kể, chứ k0 ai vì kích thước ảnh của 18mm to hơn ! Vậy thì, khi lắp 12mm vào APS-C 1.5x rõ ràng sensor nhỏ đã làm góc nhìn của ảnh bị hẹp lại đáng kể. Tỷ lệ này cũng tương đương với crop factor 1.5. Như vậy lens 12mm trên APS-C 1.5x cho ta một bức hình có view angle hẹp hơn 1.5 lần so với trên FF. Sự kết hợp này làm cho người tiêu dùng bị thiệt hại tiền đầu tư vào một lens góc rộng. 5. APS-C, FF with tele lens Nói đến một tele lens là nói đến khả năng "kéo" hình ảnh lại gần người chụp. Nói cách khác, tiêu cự càng dài thì khả năng phóng đại hình ảnh càng lớn. Tất nhiên là góc nhìn cũng bị hẹp lại, nhưng điều này thường được bỏ qua. APS-C xuất hiện, kéo theo việc những seller thường quảng cáo rằng lắp lens 200mm vào APS-C 1.5x, bạn sẽ có một tiêu cự tương đương 300mm. Và điều đó làm người dùng tưởng tượng rằng họ đang có trong tay một cái lens 300mm. Từ "tương đương" ở đây chỉ cho chúng ta 50% sự thật. Với 2 bodies FF và APS-C 1.5x, 2 lens 200mm và 300mm, chúng ta sẽ có những gì . Kích thước subject trên FF & APS-C tại 200mm Ở tiêu cự 200mm với FF ta có thể ghi được hình của 5 người đứng dàn hàng ngang lên sensor. Bây giờ cái Doppler Effect and Sonic Booms Doppler Effect and Sonic Booms Bởi: OpenStaxCollege The characteristic sound of a motorcycle buzzing by is an example of the Doppler effect The high-pitch scream shifts dramatically to a lower-pitch roar as the motorcycle passes by a stationary observer The closer the motorcycle brushes by, the more abrupt the shift The faster the motorcycle moves, the greater the shift We also hear this characteristic shift in frequency for passing race cars, airplanes, and trains It is so familiar that it is used to imply motion and children often mimic it in play The Doppler effect is an alteration in the observed frequency of a sound due to motion of either the source or the observer Although less familiar, this effect is easily noticed for a stationary source and moving observer For example, if you ride a train past a stationary warning bell, you will hear the bell’s frequency shift from high to low as you pass by The actual change in frequency due to relative motion of source and observer is called a Doppler shift The Doppler effect and Doppler shift are named for the Austrian physicist and mathematician Christian Johann Doppler (1803–1853), who did experiments with both moving sources and moving observers Doppler, for example, had musicians play on a moving open train car and also play standing next to the train tracks as a train passed by Their music was observed both on and off the train, and changes in frequency were measured What causes the Doppler shift? [link], [link], and [link] compare sound waves emitted by stationary and moving sources in a stationary air mass Each disturbance spreads out spherically from the point where the sound was emitted If the source is stationary, then all of the spheres representing the air compressions in the sound wave centered on the same point, and the stationary observers on either side see the same wavelength and frequency as emitted by the source, as in [link] If the source is moving, as in [link], then the situation is different Each compression of the air moves out in a sphere from the point where it was emitted, but the point of emission moves This moving emission point causes the air compressions to be closer together on one side and farther apart on the other Thus, the wavelength is shorter in the direction the source is moving (on the right in [link]), and longer in the opposite direction (on the left in [link]) Finally, if the observers move, as in [link], the frequency at which they receive the compressions 1/10 Doppler Effect and Sonic Booms changes The observer moving toward the source receives them at a higher frequency, and the person moving away from the source receives them at a lower frequency Sounds emitted by a source spread out in spherical waves Because the source, observers, and air are stationary, the wavelength and frequency are the same in all directions and to all observers Sounds emitted by a source moving to the right spread out from the points at which they were emitted The wavelength is reduced and, consequently, the frequency is increased in the direction of motion, so that the observer on the right hears a higher-pitch sound The opposite is true for the observer on the left, where the wavelength is increased and the frequency is reduced The same effect is produced when the observers move relative to the source Motion toward the source increases frequency as the observer on the right passes through more wave crests than she would if stationary Motion away from the source decreases frequency as the observer on the left passes through fewer wave crests than he would if stationary We know that wavelength and frequency are related by vw = fλ, where vw is the fixed speed of sound The sound moves in a medium and has the same speed vw in that medium whether the source is moving or not Thus f multiplied by λ is a constant Because the observer on the right in [link] receives a shorter wavelength, the frequency she receives must be higher Similarly, the observer on the left receives a longer 2/10 Doppler Effect and Sonic Booms wavelength, and hence he hears a lower frequency The same thing happens in [link] A higher frequency is received by the observer moving toward the source, and a lower frequency is received by an observer moving away from the source In general, then, relative motion of source and observer toward one another increases the received frequency Relative motion apart decreases frequency The greater the relative speed is, the greater the effect The Doppler Effect The Doppler effect occurs not only for sound but for any wave when there is relative motion between the observer and the source There are Doppler shifts in the frequency of sound, light, and water waves, for example Doppler shifts can be used to determine velocity, such as when ultrasound is reflected from blood in a medical diagnostic The recession of galaxies is determined by the shift in the frequencies of light received from them and has implied ...[...]... which are sufficiently and significantly distinct to place them in a separate fungal kingdom, the Kingdom Myceteae The fungi differ from the plant and animal kingdoms by their possession of a cell wall that is different 1 1043_C01.fm Page 2 Tuesday, February 17, 2004 11:23 AM 2 Mushrooms: Cultivation, Nutritional Value, Medicinal Effect, and Environmental Impact FIGURE 1.1 Cultivated mushrooms responsible... 2004 11:23 AM 4 Mushrooms: Cultivation, Nutritional Value, Medicinal Effect, and Environmental Impact FIGURE 1.4 (Color figure follows p 232.) Volvariella volvacea, showing pileus, gills, stipe, and volva FIGURE 1.5 Amanita phalloides (extremely poisonous), showing pileus, stipe, annulus, and volva The skinlike ring (annulus) may disappear with age The saclike volva is thin, rather fragile, and is usually... tendency to collapse 1043_C01.fm Page 6 Tuesday, February 17, 2004 11:23 AM 6 Mushrooms: Cultivation, Nutritional Value, Medicinal Effect, and Environmental Impact 3 Psychotropic or Hallucinogenic Poisoning Several different toxins are involved, including psilocin and psilocybin, which are found in species of Psilocybe, Conocybe, and Stropharia These compounds are similar in their reaction to d-lysergic... 11:23 AM 10 Mushrooms: Cultivation, Nutritional Value, Medicinal Effect, and Environmental Impact TABLE 1.1 World Production of Cultivated Edible Mushrooms during the Period 1981 to 1997 (× 1000 MT) Year Production Increase (%) Average Annual Increase (%) 1981 1986 1990 1994 1997 1257 2182 3763 4909 6158 — 73.6 72.5 30.5 25.4 — 14.7 18.1 7.6 8.5 Source: Data from Chang, S.T., Int J Med Mushrooms, 1,... of the mounds, nests, chambers, combs, and especially the pellets (mylospheres) 2 Identification of the fungi associated with the termites with an emphasis on the earliest developmental stages (primordia) of the fruiting body 1043_C01.fm Page 8 Tuesday, February 17, 2004 11:23 AM 8 Mushrooms: Cultivation, Nutritional Value, Medicinal Effect, Physica E 38 (2007) 109–111 Interplay between phonon confinement effect and anharmonicity in silicon nanowires M.J. Konstantinovic ´ a,b,Ã a SCK CEN, Studiecentrum voor Kernenergie/Centre d’Etude de l’Energie Nucle ´ aire, Boeretang 200, B-2400 Mol, Belgium b Institute of Physics, P.O. Box 68, 11080 Belgrade, Serbia Available online 16 December 2006 Abstract Getting light out of silicon is a difficult task since the bulk silicon has an indirect energy electronic band gap structure. It is expected that this problem can be circumvented by silicon nanostructuring, since the quantum confinement effect may cause the increase of the silicon band gap and shift the photoluminescence into the visible energy range. The increase in resulting structural disorder also causes the phonon confinement effect, which can be analyzed with a Raman spectroscopy. The large phonon softening and broadening, observed in silicon nanowires, are compared with calculated spectra obtained by taking into account the anharmonicity, which is incorporated through the three and four phonon decay processes into Raman scattering cross-section. This analysis clearly shows that the strong shift and broadening of the Raman peak are dominated by the anharmonic effects originating from the laser heating, while confinement plays a secondary role. r 2007 Elsevier B.V. All rights reserved. PACS: 78.30.Am; 78.20.Àe; 78.66.Db Keywords: Nanowires; Silicon; Raman 1. Introduction For the past 10 years, researchers have tried to coax light out of silicon, with varying degrees of success. The main problem is that the indirect energy band gap electronic structure of bulk silicon makes it not suitable for optoelectronic applications. It is expected that this problem can be circumvented by silicon nanostructuring, since the quantum confinement effect may cause the increase in the silicon band gap and shift the photoluminescence into the visible energy range. The expectation that reducing dimensions of silicon structures would turn this material from indirect into direct band gap system triggered a lot of research in the field of opt oelectronics. However, despite a large amount of research, the exact origin of the increased luminescence and a strong Raman phonon softening, reported in previous works on Si clusters [1–8], are not fully unde rstood. Recently, it was shown [12] that anharmonicity, due to the local heating effect, represents the main source of phonon softening and broadening, while the phonon confinement plays a secondary role. Here, I extend this investigation to the silicon nanowires, reanalyze the local heating effect that is always present in these kind of experiments, and compare the results with those in silicon nanoclusters. 2. Experiment The sample used in this investigation is made of an array of silicon nanowires (nanopillars, nanorods) obtained by electrochemical etching process [9]. Fig. 1 shows a scanning electron micrograph of a typical part of the sample. Nanowires are vertically aligned with a typical length of about 10 mm and a diameter of about 50–500 nm. Some nanorods are found to be detached from the non-reacted part of the silicon crystal, lying in the horizontal position on the top of the sample. Micro-Raman spectra were taken in ambient conditions with excitation from the 514.5 nm ARTICLE IN PRESS www.elsevier.com/locate/physe 1386-9477/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physe.2006.12.011 Ã Institute of Physics, P.O. Box 68, 11080 Belgrade, Serbia. Tel.: +381 11 3162190; fax: +381 11 3160346. E-mail address: konst@phy.bg.ac.yu. line of an Ar laser, using powers at the sample surface that varied from 10 to 500 Hindawi Publishing Corporation EURASIP Journal on Wireless Communications and Networking Volume 2007, Article ID 29086, 12 pages doi:10.1155/2007/29086 Research Article Burst Format Design for Optimum Joint Estimation of Doppler-Shift and Doppler-Rate in Packet Satellite Communications Luca Giugno, 1 Francesca Zanier, 2 and Marco Luise 2 1 Wiser S.r.l.–Wireless Systems Engineering and Research, Via Fiume 23, 57123 Livorno, Italy 2 Dipartimento di Ingegneria dell’Informazione, University of Pisa, Via Caruso 16, 56122 Pisa, Italy Received 1 September 2006; Accepted 10 February 2007 Recommended by Anton Donner This paper considers the problem of optimizing the burst format of packet transmission to perform enhanced-accuracy estimation of Doppler-shift and Doppler-rate of the carrier of the received signal, due to relative motion between the transmitter and the receiver. Two novel burst formats that minimize the Doppler-shift and the Doppler-rate Cram ´ er-Rao bounds (CRBs) for the joint estimation of carrier phase/Doppler-shift and of the Doppler-rate are derived, and a data-aided (DA) estimation algorithm suitable for each optimal burst format is presented. Performance of the newly derived estimators is evaluated by analysis and by simulation, showing that such algorithms attain their relevant CRBs with very low complexity, so that they can be directly embedded into new- generation digital modems for satellite communications at low SNR. Copyright © 2007 Luca Giugno et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distr ibution, and reproduction in any medium, provided the original work is properly cited. 1. INTRODUCTION Packet transmission of digital data is nowadays adopted in several wireless communications systems such as satel- lite time-division multiple access (TDMA) and terrestrial mobile cellular radio. In those scenarios, the received sig- nal may suffer from significant time-varying Doppler dis- tortion due to relative motion between the transmitter and the receiver. This occurs, for instance, in the last-generation mobile-satellite communication systems based on a con- stellation of nongeostationary low-earth-orbit (LEO) satel- lites [1] and in millimeter-wave mobile communications for traffic control and assistance [2]. In such situations, car- rier Doppler-shift and Doppler-rate estimation must be per- formed at the receiver for correct demodulation of the re- ceived signal. Anumberofefficient digital signal processing (DSP) al- gorithms have already been developed for the estimation of the Doppler-shift affecting the received carrier [3]andafew algorithms for Doppler-rate estimation are also available in the open literature [4, 5]. The issue of joint Doppler-shift and Doppler-rate estimation has been addressed as well, al- though to a lesser extent [6, 7]. In all the papers above, the observed signal is either an unmodulated carrier, or con- tains pilot symbols known at the receiver. The most common burstformatistheconventionalpreamble-payload arrange- ment, wherein al l pilots are consecutive and they are placed at the beginning of the data burst. Other formats are the mi- damble as in the GSM system [8], wherein the preamble is moved to the center of the burst, or the so-called [...]... greater profits, and ever larger returns for shareholders They naturally search for ready-made answers, for tidy plugand-play solutions that might give them a leg up on their rivals And the people who write business books — consultants and business school professors and strategy gurus — are happy to oblige Demand stimulates supply, and supply finds a ready demand Around and around we go But there’s more... recent bestsellers But that takes us only so far Once we’ve cleared away the delusions that permeate so much popular thinking about business, what then? The second thing a wise manager must do is focus on the elements that drive company performance while recognizing the fundamental uncertainty at the heart of the business world The remainder of the book, chapters 9 and 10, takes up these questions, suggesting... nothing to do with the pleasures of travel, but only with the efficiency of travel for learning They don’t seem to hear my explanation; they remain outraged They point out that I seem to be traveling all the time Why shouldn’t other people travel too? After they simmer down enough to understand the theorem, they still attack it It takes a long time to calm their passion with reason — and usually it isn’t... about the way we ask the question, or the way we go about trying to find answers, that keeps us from getting it right? The central idea in this book is that our thinking about business is shaped by a number of delusions There are good precedents for investigating delusions in business and economics Charles Mackay’s 1841 classic, Extraordinary Popular Delusions and the Madness of Crowds, chronicled the. .. presumably understand the toy industry better than you and I do Ted Williams, the great Red Sox outfielder, once said there was one thing he always found irritating: With runners on base and the opposing team’s slugger coming to the plate, the manager walks to the mound and says to the pitcher, “Don’t give the batter a good pitch, but don’t walk him,” then turns around and marches back to the dugout Pointless!... about the business world, which takes place not in a laboratory, but in the messy and complex world around us? Do business questions lend themselves to scientific investigation? Can we devise alternative hypotheses and test them with carefully designed experiments, so that we can support some explanations and reject others? In many instances, the answer is yes Plenty of business questions lend themselves... bubbles and more More recently, cognitive psychologists have identified biases that affect the way individuals make decisions under uncertainty This book is about a different set of delusions, the ones that distort our understanding of company performance, that make it difficult to know why one company succeeds and another fails These errors of thinking pervade much that we read about business, whether... business will never be understood with the precision of the natural sciences, it’s best understood as a sort of humanity, a realm where the logic of scientific inquiry doesn’t apply Well, yes and no It may be true that business cannot be studied with the rigor of chemistry or geology, but that doesn’t mean that all we have is ... 2/10 Doppler Effect and Sonic Booms wavelength, and hence he hears a lower frequency The same thing happens in [link] A higher frequency is received by the observer moving toward the source, and. .. of an aircraft, are observed on the ground after the plane has passed by 6/10 Doppler Effect and Sonic Booms Sonic booms are one example of a broader phenomenon called bow wakes A bow wake, such... observer 8/10 Doppler Effect and Sonic Booms Conceptual Questions Is the Doppler shift real or just a sensory illusion? Due to efficiency considerations related to its bow wake, the supersonic transport