A******y
发帖数: 2041 | 1 Each instrument is different. It is usually called reference wavelength.
Just turn the particular reference wavelength for 270 to off (usually set at
360 nm).
I |
|
w********u
发帖数: 90 | 2 wavelength 这么大，为啥pulse width 这么小？ 根据wavelength, 带宽估计是在1MHz
数量级，根据pulse width， 那么带宽1/pulse width 太大了吧， 估计没有啥示波器
可以搞出来啊 |
|
z*****n
发帖数: 7639 | 3 You are right on this sense. But talking about spectrum
you are wrong.
Yes we don't loss any wavelength component of the light
in the pulse, but spectrum of wave is a concept of the
shape of the wave, not exactly the wavelength inside it. |
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z*****n
发帖数: 7639 | 4 These are two different concepts.
The wavelength components combination is not the same as spectrum. Just thin
king of the pulse sent by the Tx, it
also contains all the wavelengths, but the pulse shape
is more rectangular. |
|
c*u
发帖数: 916 | 5 Of course dispersion will affect a 30 nm bandwidth pulse in 4 m of fiber,
especially if the center wavelength is not 1310 nm or it's specified
zero-dispersion wavelength. 30 nm is very wide bandwidth for most
applications. Let's say dispersion 5 ps/nm/km, then for 4 m and 30 nm, it
is almost 0.6 ps. The bandwidth is narrowed to almost 6 nm.
On the other hand, it's very rare that a fiber can't support 30 nm
bandwidth. |
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c*u
发帖数: 916 | 6 hehe, you read book too much. The light from candle and the spectra of
the candle still follows the Fourier transform. The light from candle
can be approximated as a white noise-type random process due to the
central-limit theorem (many sources are emitting independently). The
Fourier transform of the white noise is of course wide-band in the
frequency domain.
I am confused why people here got so confused about the "wavelength" and
"spectrum". Wavelength is just the x-axis of spectrum. That's |
|
A*u
发帖数: 111 | 7 i don't agree with the last couple of paragraphs
If all the wavelengths are in phase, it is the fourier transform limited
pulse.
see http://en.wikipedia.org/wiki/Bandwidth-limited_pulse
and delta frequency * delta t =constant
If they are not in phase, say due to dispersion, the above equation is not
valid any more. In a fiber, if there is no absorption and no nonlinear
effect, all the wavelength components should be preserved and no new one
should be created.The reason why it is broadend is as |
|
c******k
发帖数: 1140 | 8 You were saying if the density is higher, the higher states in the
conduction band would be occupied. That would result in a higher frequency
or a lower wavelength.
From my measurement, compared to the lasing spectrum between the middle
contact and the contact 3, the lasing wavelength from the contact 3 (1574nm)
is larger than that of the middle contact (1560nm) meanwhile the current
density of the contact 3 is higher than that of the middle contact. But this
is contrary to what you are talking |
|
c******k
发帖数: 1140 | 9 When I am injecting current to the InP lasers, I am always using a thermal-
electric cooler (TEC) control, and the setting point of temperature is 20C.
So you are saying the 14nm wavelength shift corresponds 30-40C temperature
change. But because of the TEC, I don't think so the laser device could have
so high temperature change.
I talked to my boss, and he is thinking the larger wavelength shift could be
due to the refractive index change with the increasing of injection current
.There is a pap |
|
g**h
发帖数: 15 | 10 If you increase temperature of TEC from 20C to 40C and meanwhile only add
bias on middle contact, I would expect the following:
1. Higher threshold current.
2. Lasing wavelength red shift 5~10nm.
3. The relative change of lasing wavelength from different bias schemes won'
t change much.
had
think |
|
s**g
发帖数: 66 | 11 Have you try to control temperature of the laser to achieve the right
wavelength?
TEC and control chips are available.
If you need better accuracy, make a wavelength locker.
1440nm
wafer
2 |
|
M*********m
发帖数: 2024 | 12 You need to reason with numbers. The electron mass is 0.511Mev, and if you put it into the relativistic mass formula, E=mc^2=sqrt(m0^2*c^4+p^2*c^2), you can see the energy is really high with E=0.1Gev. If you consider the de-Broglie wavelength, it is h/p, you can also see it is much smaller than the charateristic wavelength of electrons. The key is to compare with the relativistic mass formula. |
|
M*********m
发帖数: 2024 | 13 It seems lots of information is missing.... What is the laser wavelength?
What is the grating density? ITO is transparent to what wavelength... |
|
t**g
发帖数: 522 | 14 I take it that flux is the number of photons per unit time. (some people use
dkifferent definitions). if the photns are single wavelength, then power
divided by (h time frequency) is the flux. if photons are multiwavelengths,
then you need to know spectrum, it is more complicated, you probably need
measure power for each narrow wavelength window |
|
g******s
发帖数: 733 | 15 波分复用应该是 wavelength demultiplexing,和你说的Wavelength division
multiplexing应该是一样吧。 |
|
x*********l
发帖数: 594 | 16 大侠不用回答了，我已经知道了
http://en.wikipedia.org/wiki/Primary_colors
Biological basis
Primary colors are not a fundamental property of light but rather a
biological concept, based on the physiological response of the human eye to
light. Fundamentally, light is a continuous spectrum of wavelengths, meaning
that there are actually an infinite number of colors. However, the human
eye normally only contains three types of receptors called cones. These
respond to specific wavelengths of red, green, and blue li |
|
s**********8
发帖数: 25265 | 17 Optical coherence tomography (OCT) is an optical signal acquisition and
processing method. It captures micrometer-resolution, three-dimensional
images from within optical scattering media (e.g., biological tissue).
Optical coherence tomography is an interferometric technique, typically
employing near-infrared light. The use of relatively long wavelength light
allows it to penetrate into the scattering medium. Confocal microscopy,
another similar technique, typically penetrates less deeply into t... 阅读全帖 |
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f**d
发帖数: 768 | 18 这是一本计算神经科学的优秀著作，全文拷贝这里（图和公式缺），有兴趣的同学可以
阅读
如需要，我可以分享PDF文件（－－仅供个人学习，无商业用途）
From Computer to Brain
William W. Lytton
From Computer to Brain
Foundations of Computational Neuroscience
Springer
William W. Lytton, M.D.
Associate Professor, State University of New York, Downstato, Brooklyn, NY
Visiting Associate Professor, University of Wisconsin, Madison
Visiting Associate Professor, Polytechnic University, Brooklyn, NY
Staff Neurologist., Kings County Hospital, Brooklyn, NY
In From Computer to Brain: ... 阅读全帖 |
|
I***i
发帖数: 14557 | 19 http://en.wikipedia.org/wiki/Mantis_shrimp
Reasons given for powerful eyesight
The eyes of mantis shrimp may enable them to recognize different types of
coral, prey species (which are often transparent or semi-transparent), or
predators, such as barracuda, which have shimmering scales. Alternatively,
the manner in which mantis shrimp hunt (very rapid movements of the claws)
may require very accurate ranging information, which would require accurate
depth perception.
The fact that those with the ... 阅读全帖 |
|
w*******y
发帖数: 60932 | 20 Compatibility- Any PC or Laptop with a USB port, 733MHz CPU, and 64MB Memory
- Any brand 802.11g or 802.11n router using 2.4ghz wavelength
- Windows 2000, 2003, XP Home/Pro/64-Bit, Vista 32-Bit/64-Bit, Windows 7
-
NOT COMPATIBLE with Xbox 360, PS3, Blu-Ray Players, Roku Boxes, or any
device that does not run an Operating System. Also will not work with Dual
Band Routers that only broadcast N speeds on 5ghz wavelength - it is also
not compatible with any Apple Mac
SecurityThis adapter provides st... 阅读全帖 |
|
T*****T
发帖数: 640 | 21 The angular resolution of Hubble Telescope is not enough to detect such a
small targert at a distance of about 384,000 Km.
The aperture diameter of Hubble is just 2.4 m. Therefore, the angular
resolution for wavelength 500nm should be > 0.25 microRAD. And
because of the wrong manufacturing of the primary mirror, the angular
resultion of HUbble is > the resolution limit even the corrective
contact lens was added into the system. |
|
c**i
发帖数: 6973 | 22 (1) 歼-20拉开美中军事竞赛帷幕？ VOA Chinese, Jan 14, 2011.
http://www.voanews.com/chinese/news
/20110114-Challenges-Posed-by-J-20-113673394.html
Quote:
(a) 美国权威武器问题专家、莱克星顿研究所(Lexington Institute)的劳伦.汤普森博
士(Dr. Loren Thompson)说：
“我不知道中国军方是否想到了这一点，那就是，盖茨访华期间歼-20的试飞无意之中
很可能给美国的军工企业助了一臂之力。
“美国人通常对中国事务不是特别留心，但是国防部长盖茨访华期间，有关中国的新闻
，大家都很留心。而这期间，中国试飞了众人之前都认为10年之内不可能研发出的战机
，立即吸引了所有人的注意力。
"这一回，中方彻底做到了美国国内没有人能做到的，那就是，让国会重新考虑是否应
当继续生产F-22战机。
(b) 汤普森说，美方最终是否决定生产更多的F-22，目前还不好说，但是，假如决定继
续生产F-22的话，那么，F-22的主要厂家、洛克希德-马丁公司(Loc... 阅读全帖 |
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w*********g
发帖数: 30882 | 23 高歌，现任北京航空航天大学能源动力学院动力工程及工程热物理学科一级责任教授，
航空发动机气动热力国防重点实验室副主任，长期从事动力工程、工程热物理及流体力
学领域的教学与科研工作，并在基础科研和多学科的应用技术领域取得了一系列国际领
先水平的创新性科研成果。
他在1984年发明的"沙丘驻涡火焰稳定器"，获国家发明一等奖，钱学森同志称之为"一
项长中国人志气的重要发明"。该成果广泛应用于我国多种军用航空发动机中，取得了
数以亿元计的经济效益，至今仍保有先进水平。本刊记者于今年10月采访了高歌教授，
了解到了他近期从事的一些前沿科研工作的最新进展，尤其是他对龙卷风的研究及其工
程应用价值，让人耳目一新。
高歌教授在采访中提到，传统的航空发动机技术虽然还在不停地改进提高之中，但
受到原理和材料工艺上的限制，已经逐渐逼近了性能发展的极限。目前虽然涌现出一些
新型航空发动机技术，但仍然没有走出依靠压力膨胀过程来实现热功转换的思路。他强
调，人们应该另辟蹊径，寻找其他可用的工作原理。为此，他研究了自然界龙卷风的形
成与强化机制，发明了一项称为"余热增推"的技术，直接利用龙卷旋涡实现热功转换并
提取... 阅读全帖 |
|
v*******e
发帖数: 11604 | 24 看到我说得正确之处了吧：
物理原因：100% sunlight → non-bioavailable photons waste is 47%, leaving
物理原因：53% (in the 400–700 nm range) → 30% of photons are lost due to
incomplete absorption, leaving
物理原因：37% (absorbed photon energy) → 24% is lost due to wavelength-
mismatch degradation to 700 nm energy, leaving
生物原因（化学原因更准确）：28.2% (sunlight energy collected by chlorophyl)
→ 32% efficient conversionof ATP and NADPH to d-glucose, leaving
生物原因：9% (collected as sugar) → 35–40% of sugar is recycled/consumed
by the lea... 阅读全帖 |
|
l***y
发帖数: 1166 | 25 1. because it is difficult. for a long time, nobody made it.
2. he make it high efficient and has useful application.
3. the tech he used may be used in military. which might not be publish.
4. maser is similar with laser, only wavelength different. according to
your logic,
laser is not worth Nobel. |
|
D*X
发帖数: 364 | 26 从中村修二到诺奖之路
鲍海飞 2014-10-10
这几天，诺贝尔奖又成了这一年科研人员万众瞩目的时候了，而诺贝尔物理奖更是重中
之重，今年诺贝尔物理奖授予了日本的科学家Isamu Akasaki（赤崎勇）, Hiroshi
Amano （天野浩）和 Shuji Nakamura（中村修二），其主要工作是成功研制出一种有
效的、环境友好的光源---蓝光发光二极管（Staffan Normark (2nd L), permanent
secretary of the Royal Swedish Academy of Sciences, announces the winners of
the 2014 Nobel Prize in Physics, at the Royal Swedish Academy of Sciences
in Stockholm, capital of Sweden, Oct. 7, 2014. Isamu Akasaki and Hiroshi
Amano of Japan and Japanese-born U.S. scientist Shuji Naka... 阅读全帖 |
|
a*****y
发帖数: 33185 | 27 Two of Japan's chip companies have decided to grow lettuce and other
vegetables in idle semiconductor clean rooms, using specialized lighting to
replace sunlight.
The clean-room environment is dust-free and germ-free, as it would be for
the production of integrated circuits. As a result, no pesticide is used,
and the lettuce stays fresher for longer.
Fujitsu Semiconductor and Toshiba Corp have both started to grow greens and
believe the tightly controlled conditions produce superior plants that ... 阅读全帖 |
|
c*******2
发帖数: 617 | 28 美国证谣了， F－22很容易被发现
1. 如果挂了副油箱， 飞机就不再隐形
2. 或者如果加装a Luneburg lens，飞机也很容易被发现。
3. 就算隐形， 也只是针对雷达的 C, X, Ku and the top part of the S bands.
S or L band的雷达可以很容易发现F－22或F35， J20， J31. 美军不怕这种雷达，
因为这种雷达无法精确引导导弹。
Typically, however, those lower-frequency radars do not provide what
Pentagon officials call a “weapons quality” track needed to guide a
missile onto a target. “Even if you can see an LO [low observable] strike
aircraft with ATC radar, you can’t kill it without a fire control system,”
an Air Force... 阅读全帖 |
|
m***6
发帖数: 884 | 29 sounds fishing.
However, some evidences seem to indicate that the J20 airplanes generated
recognizable reflective electromagnetic waves when the wavelength is within
450nm to 700nm. The Taiwan independence army has vowed to make great use of
this finding in its next generation of radar system powered by biological
love (making) process. |
|
r****t
发帖数: 212 | 30 计划轨道就是514公里
The main goal today was getting the Paz satellite aloft for Spanish operator
Hisdesat. If all goes according to plan, Paz will observe Earth in radar
wavelengths from a 319-mile-high (514 kilometers) perch in quasi-polar orbit
, |
|
发帖数: 1 | 31 飞的比计划更高
说明火箭好推理大
: 计划轨道就是514公里
: The main goal today was getting the Paz satellite aloft for Spanish
operator
: Hisdesat. If all goes according to plan, Paz will observe Earth in
radar
: wavelengths from a 319-mile-high (514 kilometers) perch in quasi-polar
orbit
: ,
|
|
s*x
发帖数: 8041 | 32 Avatar
John Springer • 14 hours ago
Just read how Russia built second pipeline to China and no longer using
dollars , but petro yuans and rubles. We can no longer simply use threat of
sanctions and tariffs. We can negotiate but must treat our peers, even those
who see the world differently, as participants or we will fail.
6
•Reply•
Avatar
Orange Juice John Springer • an hour ago
Who will buy our debt if we upset China? Trump arranged for record deficits
and he's trying... 阅读全帖 |
|
发帖数: 1 | 33 Erwin Schrödinger
Born: 12 August 1887, Vienna, Austria
Died: 4 January 1961, Vienna, Austria
Affiliation at the time of the award: Berlin University, Berlin, Germany
Prize motivation: "for the discovery of new productive forms of atomic
theory"
Field: quantum mechanics
Prize share: 1/2
Work
In Niels Bohr's theory of the atom, electrons absorb and emit radiation of
fixed wavelengths when jumping between fixed orbits around a nucleus. The
theory provided a good description of the spectrum cr... 阅读全帖 |
|
t******i
发帖数: 215 | 34 光斑大小的计算见：
http://en.wikipedia.org/wiki/Rayleigh_length
we basically need a collimated laser beam, whose Rayleigh range (zR) is
300km/2 = 150km. assuming wavelength = 1um, then beam radius at waist (w0)
is about 0.2-0.3 m. So at target, the beam radius cannot be larger than 0.5
m. 就是说直径是小于1m的。
以上如有错误请指正。
1m |
|
d********e
发帖数: 2221 | 35 I'm not 100% sure but 90% sure. this kind of thing usually does "push broom
" scanning. each scan line is usually perpendicular to the orbital
direction. each scan line is spread in the orbital direction and projected
to to a 2-D sensor array. It does not make sense to have only a few
wavelengths because there is already a 2-D sensor array.
http://en.wikipedia.org/wiki/Hyperspectral_imaging |
|
p****s
发帖数: 3184 | 36 No. The formula (5) is a point-to-point one. Earth curvature is irrelevant
here.
目标截面面积δ = 5000m^2 which is of a Nimitz-class carrier (length 333m *
height 15m).
雷达发射功率Pt (cm) = Pt (mm) = 50kW, which is about the max value you can
put into a missile's warhead
天线增益Gt (cm) = Gr(cm) = Gt (mm) = Gr(mm) = 26dBi
Here is a 27dBi 5.8GHz (wavelength ~=5cm 厘米波) directional antenna on
taobao
http://item.taobao.com/item.htm?spm=a230r.1.14.40.Pfeg8g&id=390
1&abbucket=8#detail
It's about the max size you can... 阅读全帖 |
|
N*V
发帖数: 350 | 37 【 以下文字转载自 Military 讨论区 】
发信人: wayofflying (小破熊), 信区: Military
标 题: 人类第一台真空能发动机即将在中国攻关成功
发信站: BBS 未名空间站 (Sat May 14 22:28:25 2011, 美东)
高歌，现任北京航空航天大学能源动力学院动力工程及工程热物理学科一级责任教授，
航空发动机气动热力国防重点实验室副主任，长期从事动力工程、工程热物理及流体力
学领域的教学与科研工作，并在基础科研和多学科的应用技术领域取得了一系列国际领
先水平的创新性科研成果。
他在1984年发明的"沙丘驻涡火焰稳定器"，获国家发明一等奖，钱学森同志称之为"一
项长中国人志气的重要发明"。该成果广泛应用于我国多种军用航空发动机中，取得了
数以亿元计的经济效益，至今仍保有先进水平。本刊记者于今年10月采访了高歌教授，
了解到了他近期从事的一些前沿科研工作的最新进展，尤其是他对龙卷风的研究及其工
程应用价值，让人耳目一新。
高歌教授在采访中提到，传统的航空发动机技术虽然还在不停地改进提高之中，但
受到原理和材料工艺上的限制，已经逐渐逼近了性能发... 阅读全帖 |
|
U*****g
发帖数: 366 | 38 My area: semiconductor device and physics / electrical engineering
CV:
QIUGUI ZHOU
Email: q**[email protected]
Phone: 1+(434) 243-2147
===========================================================================
EDUCATION
UNIVERSITY OF VIRGINIA
Charlottesville, VA
Ph.D. in Electrical Engineering
2011
UNIVERSITY OF SCIENCE AND TECHNOLOGY OF CHINA(中国科学技术大学)
Hefei, CHINA
Master of Science in Optics ... 阅读全帖 |
|
m****1
发帖数: 736 | 39 http://www.nae.edu/Projects/MediaRoom/20095/130169/130172.aspx
New Members
Atwater Jr., Harry A., Howard Hughes Professor of Applied Physics and
Materials Science, California Institute of Technology, Pasadena. For
contributions to plasmonics.
Balakrishnan, Hari, professor of computer science, Massachusetts Institute
of Technology, Cambridge. For contributions to wired and wireless networks
and distributed systems.
Bardasz, Ewa A., president, ZUAL Associates Consulting, Mentor, Ohio. For
novel au... 阅读全帖 |
|
r******t
发帖数: 8967 | 40 【 以下文字转载自 EE 讨论区 】
发信人: yuverson221 (), 信区: EE
标 题: 跪求前辈内推Semiconductor Process Engineer，entry level的工作
关键字: 半导体，工作
发信站: BBS 未名空间站 (Fri Jan 20 16:56:26 2017, 美东)
小弟是刚毕业的硕士学生。在实验室主要是做Graphene solar cell的，有两年的实验
室经验，已经thesis答辩完，马上准备发paper。最近找工作找的快崩溃了，求相关的
公司的前辈，帮忙内推。
贴上我的工作经历。
• At UIC, my thesis research focus is to develop transfer-free
graphene-on-silicon heterojunction solar cells and plasmonics enhancement of
photo-conversion efficiency and received 1.5% PCE
• Tested and op... 阅读全帖 |
|
n**********o
发帖数: 1016 | 41 https://www.nae.edu/MediaRoom/178117.aspx
Abadi, Martín, principal scientist, Google Inc., Palo Alto, Calif. For
contributions to the formal theory of computer security.
Abrahamson, Norman A., chief engineering seismologist, Pacific Gas &
Electric Co., Piedmont, Calif. For contributions to seismic hazard
assessment and for leadership in engineering seismology and earthquake
engineering.
Adams, Robert W., senior fellow, Analog Devices Inc., Acton, Mass. For
contributions to digital storage and... 阅读全帖 |
|
s*******i
发帖数: 1063 | 42
~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~ here the scattered light is due to difference in refractive
index.
You can try, even with 150 nm emulsions, you will still see white, but it is
much smaller than wavelength of visible light. |
|
D**********s
发帖数: 3139 | 43 算了，今天耐心不太好，花时间研究了提议也没什么人捧场。
如果要去掉vibration，网上推荐和卖的那些damper都不太实际。因为既要考虑到管子
的散热，又要隔音。这在物理上是非常难做到的，声音和热在固体中都是phonon传播的
，热的传导涵盖了short to long wavelength。用简单设计做一个既隔音又导热的
filter不是很容易。那些正在卖的和网上说有用的硅胶和海绵之类的，基本都是玩闹，
要不让散热更差，要不根本就是transparent to vibration。很多的震动都是通过PCB和
管座传入的。
又是我的愚见，别认真。
can |
|
G****o
发帖数: 229 | 44 我在听，目前主要是讲如何推箱子
project是做 guitar amp 估计都是重点在做音箱吧
Week 1
Lesson 1: Introduction to wave propagation, simple oscillating systems,
sound pressure, sound waves, the speed of sound, wavelength, frequency and
wavenumber, sound pressure level, and auditory directional cues.
Lesson 2: Electronics fundamentals - charge, current, voltage, resistance,
Ohm’s law, DC circuits, finding currents and voltages in simple circuits
Week 2
Lesson 1: Reflection and absorption of sound, resonances in air columns,
res... 阅读全帖 |
|
m***y
发帖数: 14763 | 45 It's not distance, this meter doesn't work on that wavelength. |
|
m**n
发帖数: 9010 | 46 on what "wavelength"?
整天闹"辐射"的同学讲的"辐射", 当然不是微波自己跑出
微波炉, 而是微波炉工作时的电磁波. 这个当然可以测.
(自然, 很多辐射爱好者未必分得那么清楚而已, 所以才会
听到"微波炉"的"辐射"就开始害怕自己象被微波煮熟了一样) |
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s****9
发帖数: 23 | 47 这种辐射的波长（wavelength）比较长，穿透力小。大部分被墙吸收了。
安心睡觉。 |
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s*i
发帖数: 5025 | 48 对中年大叔烧瓶具有相当的指导作用。
[发表自未名空间手机版 - m.mitbbs.com] |
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