l**n
发帖数: 67 | 1 Einstein's field equation
Now that we have known that the curvature of the space-time is
equivalent to a gravitation field, we are one step away from
the Einstein's field equation. The one left question is how
can we relate the gravitation field to the matter in the
universe. Different people can have different idea how to
construct this matter to gravitation field relation, but there
is one thing we should keep in mind. Newton told us centuries
ago how the gravitation field looks like for a mas |
|
t*****y
发帖数: 30 | 2 I am using linear multiregression to fit my data
ie y=ax1+bx2+cx3+dx4+ex5+fx6+g
The final R squre from the fitting is 81.94%. It is also the correlation
coefficient of experimental y and fitted y, which can be plotted.
I am wondering if there is nonlinearity buried in the data since 81.94% is
not very high.
But from the plot, I couldn't see very obvious curvature. But even if
the real relationship is nonlinear, it should be a curved plane in 6
dimensional space. I suppose I am not able to visul |
|
f*******d
发帖数: 339 | 3 but in your example, you and the girl met at North pole has
nothing to
do with gravitational attraction: you and the girl are not
attracting
each other:-)
A better? example could be this: suppose you and a girl are
rolling on a
huge springy net. This net is initally hanging flat, but the
place where
you or the girl stays is bent down due to the weight. After
a while,
you found you and the girl gradually come togather to the
center of the net, because "curvature". |
|
l**n
发帖数: 67 | 4 Absolutely, you are right. It's the space-time curvature
which corresponds to gravity. But it is rather obsure
to give an example in four or more dimensions since you
will have problem to visualize it and the key point here
which i use the word brilliant is the equavelence of
a force to the geometric property of something. The
example of fisherdad about the rubber sheet is rather
obscure to me because when you put some massive particle
on the rubber sheet, it actually cause the sheet bend
in the |
|
l**********n
发帖数: 72 | 5 I think it's concrete and beautiful.
"Quantum gravitation effects are usually ignored in calculations of the
formation and evolution of balck holes. The justification for this is that the
radius of curvature of space-time outside the event horizon is very large
compared to the Planck length (Gh/c^3)^1/2~10^-33 cm, the length scale on
which quantum fluctuations of the metric are expected to be of order unity.
This means that the energy density of particles created by the gravitation
field is smal |
|
d*****r
发帖数: 4 | 6 Yes, light has both wave-like and particle-like properties. But you don't
need to calculate the rest mass of a photon, because it's always 0.:)
I never learned that the speed of photon becomes slower in a gravitational
field. Can you tell me which book you read?
About why light cannot escape from a black hole, it's a GR effect. It's
related to the curvature of spacetime in a gravitational field. Actually,
I am not understand it well. You can read some textbooks of GR. Also, there
is useful expla |
|
w****o
发帖数: 20 | 7 Using k.P method, you find that approximately the electron effective mass at
the bottom of the conduction band is given by,
M0/Me* ~ 1 + EB/Eg.
So for Eg<>EB, Me* ~ M0.
The physics is that the conduction band and valence band tend to repell each
other. When they are closer (Eg smaller), the dispersion of bands is repelled
more strongly such that they have larger curvature, corresponding to smaller
effective mass.
For metals, the real effective electron mass that you measure |
|
c*****t
发帖数: 198 | 8 【 以下文字转载自 Biology 讨论区 】
发信人: compact (support), 信区: Biology
标 题: Paper help
发信站: BBS 未名空间站 (Sat Aug 21 00:38:52 2010, 美东)
Q Rev Biophys. 2010 Aug 9;:1-75
Rate theories for biologists.
Huan-Xiang Zhou
Q Rev Biophys. 2010 Feb ;43 (1):65-158 20667175
Structures of membrane proteins.
Kutti R Vinothkumar, Richard Henderson
MRC Laboratory of Molecular Biology, Cambridge, UK.
Q Rev Biophys. 2010 May 18;:1-41 20478077
DNA curvature and flexibility in vitro and in vivo.
Justin P Peters, L James Maher |
|
A*******s
发帖数: 3942 | 9 it's a judgmental call. linear models are everywhere but u can always
include curvature into ur models as long as it makes sense. |
|
A*******s
发帖数: 3942 | 10 it's a judgmental call. linear models are everywhere but u can always
include curvature into ur models as long as it makes sense. |
|
A*******s
发帖数: 3942 | 11 u mean no significant linear correlation between Y and X? Then changing the
link function of Y wouldn't help much. try to transform X, say introducing
curvature. or even find new X variables.
or dichotomizing Y into depressed and non-depressed using different
thresholds. sometimes it helps.
0 |
|
A*******s
发帖数: 3942 | 12 google "bounded outcome regression". As far as i know, latent variable model
or beta regression can be applied.
i dont think it is about lack of curvature. I bet LZ would see the same
pattern even after he add quadratic terms.
it is ok to use OLS in the case if only the conditional mean of Y is of
interest and variance is nuisance. Whenever u would like to draw inference
from the distribution of Y (significance test, confidence interval), OLS
would fail since it gives wrong estimate of VAR[Y|X] ... 阅读全帖 |
|
p********a
发帖数: 5352 | 13 ☆─────────────────────────────────────☆
cici (full house) 于 (Mon Nov 7 08:33:47 2011, 美东) 提到:
对于logistic regression
log（pi/1-pi）=b0+b1x1+b2x2
我现在已知independent variables和response variable{log(pi/1-pi)}
我要怎么做才能把参数b0,b1,b2 fit出来？非常感谢
☆─────────────────────────────────────☆
sleephare (I+don't+know.) 于 (Mon Nov 7 14:16:38 2011, 美东) 提到:
SAS, R?
☆─────────────────────────────────────☆
cici (full house) 于 (Mon Nov 7 16:19:05 2011, 美东) 提到:
R,thanks
☆────────────────────────────────────... 阅读全帖 |
|
c*******o
发帖数: 8869 | 14 用logistic regression 得到了predicted probability(for case=1), 结果在
predicted likelihood 很高 (0.8-1) 的区间 和很低的区间 （0-0.1), case
enrichment 很高， 而在中间区 （0.5左右）， case 的比例很底， 为什么predicted
likelihood 会有这种curvature的情况， 如何处理？
跪谢了。 |
|
l*******s
发帖数: 197 | 15 在2X2factorial design中，加入4个中心点数据,如何用SAS分析出其curvature？
多谢！
注：按定义可以笔算出来，但是想用SAS Code一步到位。 |
|
k********n
发帖数: 756 | 16 If I go to gym, I fall in love immediately with the wonderful curvatures I
see from the side or behind. Therefore, I just stare at them and then get
tired of them completely in 5 seconds. |
|
x********0
发帖数: 190 | 17 1. There is slight reversal of lordosis at the L1-L2 level and possibly
some very subtle dextroscoliotic curvature of the lumbar spine. Correlation
with plain film scoliotic series may be helpful as clinically indicated.
2. There is borderline congenital narrowing of the central canal along
the course of the mid to distal lumbar spine, however with no significant
central stenosis at any level .
3. At L5-S1 there is mild posterior annular disc bulging/diffuse endplate
spurring with slig... 阅读全帖 |
|
g****f
发帖数: 5 | 18 我同学的女儿，13岁，刚被诊断胸椎侧弯。北京的医院有的建议保守治疗，有的建议赶
紧手术。考虑手术的风险，父母十分担心。望熟悉这方面的朋友可以帮忙建议。十分感
谢。 如果可以介绍美国这边的医院也十分感谢。
MR检查报告单
胸椎平扫
扫描技术：Cor、 Sag、T1WI、T2WI
检查所见：胸椎稍显侧弯，以Th2为中心向左突，Cobb角约19.48°，胸椎生理曲度存在
，椎体及附件未见明显骨质增生征象，椎间隙未见明显狭窄，未见明显椎间盘膨出或突
出征象，胸段脊髓未见明显异常号影。
意见：胸椎稍显侧弯，以Th2为中心稍向左突，请结合临床。
MR examination report
T-spine Routine Scan
Scanning Technology: Cor、Sag、T1WI、T2WI
Examination findings: Thoracic vertebrae are showed T2-centered left
scoliosis. The Cobb angle is about 19.48°. Physiological curvature of
thorac... 阅读全帖 |
|
w*******y
发帖数: 60932 | 19 Please accept my apologies if this is a repost. All the threads are making
me dizzy
Oakley Montefrio Sunglasses
24.00 plus 6.95 flat rate ship, free over $100
Link:
http://www.6pm.com/search/brand/394/filter/categoryFacet/"Eyewear"/productTypeFacet/"Eyewear"/priceFacet/"$50.00 and Under"/sort/price/asc
Whether you're out at a family barbecue, rollerblading at the beach, or just
nursing your hangover, these sunglasses are the perfect accessory for you.
Frames made to be lightweight and long-lasti... 阅读全帖 |
|
w*******y
发帖数: 60932 | 20 Right Here:
http://www.6pm.com/oakley-felon-matte-black-w-grey?2424
# Make bad look good without actually committing a crime in these Oakley
Felon sunglasses.
# Durable and lightweight C-5 metal frame also allows for continuous comfort
, because looking good doesn't need to hurt bad.
# Frame is built with a Three-Point Fit that ensures optical alignment.
# Plutonitelenses provide protection from all forms of harmful light.
# Protection from all angles due to the unique curvature of the lens.
# A... 阅读全帖 |
|
w*******y
发帖数: 60932 | 21 Link at 6pm:
http://www.6pm.com/search/brand/394/filter/productTypeFacet/"Eyewear"/sort/price/asc/
10% code 6PMLC2010 Selma!
Product Information:
Make bad look good without actually committing a crime in these Oakley
Felon sunglasses.
Durable and lightweight C-5 metal frame also allows for continuous comfort,
because looking good doesn't need to hurt bad.
Frame is built with a Three-Point Fit that ensures optical alignment.
Plutonitelenses provide protection from all forms of harmful light.
Pro... 阅读全帖 |
|
w*******y
发帖数: 60932 | 22 Link:
http://www.amazon.com/gp/product/B002EL32US/ref=s9_simh_gw_p309
Lowest price I've ever seen for these. Bought them a few months back at $58,
also from amazon. The $48.46 model is the polished black frame/gray lenses.
Pretty nice, but the matte black frame with iridium lenses are my favorite.
NOT POLARIZED!
If the world wasn't made to fit you, you're in good company. The legends of
action sports go through life reveling in originality and crushing
conventional ideas beyond recognition. If o... 阅读全帖 |
|
B******y
发帖数: 2255 | 23 In finance, a strangle is an investment strategy involving the purchase or
sale of particular option derivatives that allows the holder to profit based
on how much the price of the underlying security moves, with relatively
minimal exposure to the direction of price movement. The purchase of
particular option derivatives is known as a long strangle, while the sale of
the option derivatives is known as a short strangle. It is related to a
similar option strategy known as a straddle. If a big move... 阅读全帖 |
|
B******y
发帖数: 2255 | 24 In finance, a strangle is an investment strategy involving the purchase or
sale of particular option derivatives that allows the holder to profit based
on how much the price of the underlying security moves, with relatively
minimal exposure to the direction of price movement. The purchase of
particular option derivatives is known as a long strangle, while the sale of
the option derivatives is known as a short strangle. It is related to a
similar option strategy known as a straddle. If a big move... 阅读全帖 |
|
p**********g
发帖数: 9385 | 25 What is your curvature? |
|
p**********g
发帖数: 9385 | 26 I have some spare -3.25 contacts。
But I don't know what your curvature is. |
|
n*n
发帖数: 1378 | 27 contact 难道不是买了合适的度数就可以带的么？还要测什么curvature??!! |
|
o******r
发帖数: 259 | 28 Level set method was first proposed by Osher and Sethian in 1987
It has been extensively studied and widely used in image processing
Below is the most important papers on level set I used in drafting my pa
per.
[1] Stanley Osher, James A. sethian, Fronts Propagating with Curvature D
ependent Speed: Algorithms Based on Hamilton-Jacobi Formulations, Journa
l of Computaitonal Physics, 79, pp.12-49, (1988).
[2] Ravikanth Malladi, James A. Sethian, Baba C. Vemuri, Shape Modeling
with Front Pr |
|
m*****o
发帖数: 17 | 29 Hi,romel, thanks a lot for your suggestion. I guess the mean curvature flow
you suggested is level-set method related implicit surface. If my guess were
right, would the speed very slow? Thanks again.
better, |
|
r***l
发帖数: 36 | 30 what I was suggesting is mesh-based, but level set doesn't have to be slow
either.
It is indeed an iterative method, but it's not slow.
What you need to compute is a gradient flow, the graident of total surface
area, and on a surface, it means the vertex needs to follow (1/A_x)dA/dx,
you should be able to find the details for mean curvature flow on meshes.
flow
were |
|
h***i
发帖数: 427 | 31 有没有好的link或paper,最好有matlab codes. 呵呵。thx. |
|
