h******y
发帖数: 26 | 1 Some friend asked me the following question:
For a real scalar field \phi, assume that H = H_free - \int d^3\ x J \phi. J
(x, t) is just some real number, source, or background field, without second
quantization. Now, what is the amplitude \psi(x, t) for finding a particle
at time t(before, during, or after source is on/off) at position x? The J(x,
t) is nonzero only for finite period of time. And the initial state is
vacuum, when t --> -\infty
This question looks simple. However, I cannot find |
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C********n
发帖数: 6682 | 2 or why gauge it
通常大家谈论物理，都有些大前提，比如经典力学的f=ma ,电动的
F_\mu\nu,量子力学里的薛定谔方程
这些东西都是猜出来的
实际上任何关于相互作用的理论都是猜出来的
那么如何猜测相互作用的形式，这是物理学的最大的基本问题
在weyl之前，大家基本是胡猜的，无论是牛顿力学还是经典电动力学
后来weyl发现，量子力学里，通过引入gauge变换不变形的要求,可以加入
最小作用原理(D_\mu->D_\mu + ieA),直接可以在量子力学里引入电磁相互
作用，于是他天才的想到，也许局域化的连续对称性是引入相互作用的好
办法
这个思想经过pauli ,klein, CN yang等人的发展，经过弱电和强作用的实验验证
被确认为是引入相互作用的有效办法
但gauge并不是唯一的引入相互作用的办法，其他的办法也很多，gauge的一个好处是
通过higgs机制，即使是有质量的 gauge field,也是可以重整化的
换句话说，从目前来看，你写出四维空间的一个可重整化的拉式量，其组合必然是一些
规范场fermi子和一些scalar boson的组合
说这么多，g |
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j*********g
发帖数: 3179 | 3 They are free electrons/holes traveling in periodic field. who said they are
bonded? Depending on band structure and which state electrons occupy,
effective mass are vastly different. The masses you quote are just mass at
bottom of conduction band and top of the valence band. Even at top of the
valence band, there are usually heavy holes and light holes. Even for a
single state, effective mass is a tensopr, not scalar. |
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m*******r
发帖数: 98 | 4 The current version of MPB supports complex epsilon tensor
The current version of MEEP does support complex epsilon scalar
The future version will incorporate complex epsilon and mu tensor
learn |
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w***3
发帖数: 1469 | 5 gauge field dual to strings.
Wilson loop is dual to string amplitude
Maldacena-Wilson loop gives a precise correspondence when the system
contains scalar fields and N=4.
看到一个Maldacena的id,能不能给详细解一下这的是怎么对应的 |
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Q******g
发帖数: 607 | 6 pion is pseudo-scalar.
(-1)(-1)(-1)=/=(-1)(-1) |
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l******o
发帖数: 298 | 7 pion is pseudo-scalar.
(-1)(-1)(-1)(-1)=(-1)(-1)
如果theta能衰变出4个pai粒子，而tao能衰变出2个pai粒子。
就可以说对称了吗？ |
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w*******e
发帖数: 15912 | 8 [转载] 看看中国的落后的物理科研现状，多么可怕！
作者: xylang (站内联系TA) 发布: 2005-12-06
review of modern physics 可谓是物理学界之至高无上无克配敌的刊物，从１９２９
年到现在共只有２７５３篇次的文章被发表，可见其分量多重啊，比起physical
review seriers 和 PRL 都高级很多啊，我一个南京大学的同学说就他们学校的一个
做群论的叫做陈金全的教授发过一次，并且他后来有可能再被邀请发一次，不幸他过早
的去世了，然后中国（至少内地）就没有一个发过这个东西。陈金全的那本名作我是有
的，是在北京遇到南京大学的一个博士，很好的一个人——一个很帅的大哥送给我的，
可惜我没有看，他从南京寄给我，当是真的很感动啊。
今天搜索了一下，结果如下：
首先，Set affiliation as "china", 发现如下２结果：
１）Quasinormal-mode expansion for waves in open systems
E. S. C. Ching, P. T. Leung, A. Maassen van de... 阅读全帖 |
|
w*******e
发帖数: 15912 | 9 [转载] 看看中国的落后的物理科研现状，多么可怕！
作者: xylang (站内联系TA) 发布: 2005-12-06
review of modern physics 可谓是物理学界之至高无上无克配敌的刊物，从１９２９
年到现在共只有２７５３篇次的文章被发表，可见其分量多重啊，比起physical
review seriers 和 PRL 都高级很多啊，我一个南京大学的同学说就他们学校的一个
做群论的叫做陈金全的教授发过一次，并且他后来有可能再被邀请发一次，不幸他过早
的去世了，然后中国（至少内地）就没有一个发过这个东西。陈金全的那本名作我是有
的，是在北京遇到南京大学的一个博士，很好的一个人——一个很帅的大哥送给我的，
可惜我没有看，他从南京寄给我，当是真的很感动啊。
今天搜索了一下，结果如下：
首先，Set affiliation as "china", 发现如下２结果：
１）Quasinormal-mode expansion for waves in open systems
E. S. C. Ching, P. T. Leung, A. Maassen van de... 阅读全帖 |
|
w*******e
发帖数: 15912 | 10 印度比天朝物理强不少啊。
[转载] 看看中国的落后的物理科研现状，多么可怕！
作者: xylang (站内联系TA) 发布: 2005-12-06
review of modern physics 可谓是物理学界之至高无上无克配敌的刊物，从１９２９
年到现在共只有２７５３篇次的文章被发表，可见其分量多重啊，比起physical
review seriers 和 PRL 都高级很多啊，我一个南京大学的同学说就他们学校的一个
做群论的叫做陈金全的教授发过一次，并且他后来有可能再被邀请发一次，不幸他过早
的去世了，然后中国（至少内地）就没有一个发过这个东西。陈金全的那本名作我是有
的，是在北京遇到南京大学的一个博士，很好的一个人——一个很帅的大哥送给我的，
可惜我没有看，他从南京寄给我，当是真的很感动啊。
今天搜索了一下，结果如下：
首先，Set affiliation as "china", 发现如下２结果：
１）Quasinormal-mode expansion for waves in open systems
E. S. C. Ching, P. T. Leung, A. M... 阅读全帖 |
|
l***y
发帖数: 1166 | 11 The Earth OEMII thinks of Space as a " scalar continuum " in all directions.
From this image of space, you worked out (initiated by Euclid) a whole
geometry based on abstractions such as the point, the line, and the plane.
You finished by accepting that POINT, LINE and PLANE really represent the
true components of the WAAM, although using a mental abstraction.
This original vice, not yet corrected, is costing you a considerable delay
in the comprehension of the physical world.
Indeed: when you i... 阅读全帖 |
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s*******r
发帖数: 63 | 12 1. Suppose we bid x, x\in[0,1], the profit can be given by
P = (1.5V-x)*\delta_{x-V},
where \delta_{x-V} is the unit step function, \delta(x)=1 for x>=0, 0 for x<
0. Here, note that x is a scalar and V is a random variable.
we want to max E[P]=E[(1.5V-x)*\delta_{x-V}]=-x^2/4, thus x=0. shouldn't bid
anything.
PS:
E[(1.5V-x)*\delta_{x-V}] = \int_0^1 (1.5V-x)*\delta_{x-V} dV
= \int_0^x (1.5V-x) dV
= -x^2/4
2. suppose there are x statements are true, then 1st,...,nth statements are
false and the re |
|
i*****r
发帖数: 1302 | 13 我一直用&&和||,但今天用&&的时候,告诉我
Operands to the || and && operators must be convertible to
logical scalar values.
我读了help文件,还是没看明白 |
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S*********g
发帖数: 5298 | 14 >> help rem
REM Remainder after division.
REM(x,y) is x - n.*y where n = fix(x./y) if y ~= 0. If y is not an
integer and the quotient x./y is within roundoff error of an integer,
then n is that integer. The inputs x and y must be real arrays of the
same size, or real scalars.
By convention:
REM(x,0) is NaN.
REM(x,x), for x~=0, is 0.
REM(x,y), for x~=y and y~=0, has the same sign as x.
Note: MOD(x,y), for x~=y and y~=0, has the same sign as y.
|
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u**x
发帖数: 45 | 15 I learned the concept of norm long time back, but have been coming across it
frequently. So let me try to recite what I learned.
矩阵范数的定义是与矢量空间的内积和范数的相联系的
矢量空间的范数的定义是: ||||: X->R s.t.
1) ||x||>=0, for any x b.t. X and ||x||=0 iff x=0
2) ||ax||=|a|||x||, for any vector x b.t. X , and scalar a b.t. C
3) ||x+y||=||x||+||y||, for any x, y b.t. X.
当矢量空间, X=C^n 时, 复矢量的欧氏范数可定义作 ||x||2=(x,x)^(1/2)
更广义的, n 维复矢量的Holder范数的定义是
||x||p=(sigma(|xi|^p, {i,1,n}))^(1/p)
其中P为2时, 它就是欧氏范数. 另外p=1, p=inf也是常用范数. 通常它们 |
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B***y
发帖数: 83 | 16
scalar.
这题目在3-维下的罢？
Without loss let |a| = 1, a unit vector. then
let y = y1 a + b, where a and b is orthogonal.
then y \dot a = d = y1,
y \corss a = b \corss a = c
thus c \cross a = -b ,
so y = d a - c \cross a.
now if |a| \ne 1, then the result is
y = \frac{d a }{|a|^2} - c \cross \frac{a}{|a|^2}, i.e, differs by a
factor of |a|^2. |
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s***e
发帖数: 911 | 17
Oh...
Div(p*q)=d_i(p*q_i)=p*d_i(q_i)+(d_i(p))*q_i=p*div(q)+grad(p) \dot q
Where p is a scalar, q is a vector, and d_i is the derivative respect to
the i-th coordinate. Repeated index means summation.
We have already express q by derivative of x(a,t), so replace p by \rho u
get the result. |
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l**n
发帖数: 67 | 18
irrotational->\vec{v} = \div{phi} which is defined by you
incompressible->\laplace{phi}=0???(no source,sink)
by definition, kinetic energy is
\int_V \rho/2*(\grad{phi})^2 dV
= \rho/2*\int_V{(\grad{phi})^2}dV
= \rho/2*\int_V{\phi*\laplace{phi}+(\grad{phi})^2}dV
using Green's first identity
= \rho/2*\int_s{\phi*\vec{n}.\grad{\phi}dA}
= \rho/2*\int_s{\phi*\partial{\phi}/\partial{n}}dA
The green's first identity is:
for any well-behaved scalar function a,b,
\int_V{a\laplace{b}+\grad{a}.\grad{b})dV |
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i*******n
发帖数: 166 | 19
"Virial" was coined by R. Clausius who first proved the scalar virial
theorem in 1870. Clausius called the integral corresponding to the
-0.5 \times the trace of the potential energy tensor "viral" ((i.e. -0.5
\times the total potential energy).
br /> |
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h****a
发帖数: 234 | 20 use "retarded potential" ya...
phi(r,t)=1/(4pi) \int(d3r' \rho(r',t-|r-r'|/c) / |r-r'|)
A(r,t)=1/(4pi) \int (d3r' \j(r',t-|r-r'|/c)/|r-r'|)
where phi(r,t) and A(r,t) are the scalar and vector
potentials
(in Lorentz gauge), and
\rho(r,t) and j(r,t) are the charge and current densities,
for point particle
\rho(r,t)=q delta(r-R(t))
j(r,t)= q v(t)delta(r-R(t))
where R(t) is the trajectory of the electron.
Readily derivable from the above. |
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M*********m
发帖数: 2024 | 21
True for isotropic medium. But if there is an interface between different
media, the TE and TM mode transmission would be quite different due to the
boundary conditions. Normally for 2D PC structure, it's enough to separate the
problem into TE and TM mode, basically the electric field is inplane or
vertical to the dielectrics and they are still a scalar wave. But if you
consider the surface roughness of the holes, the radiation loss, you will have
to use vector electromagnetic theory. Mostly in |
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y***u
发帖数: 25 | 22 kaka, my question was: if as u said:
"One fundamental
then, in SUSY, how to explain? If I remember correctly, gauginos can also be
the media of interractions in SUSY. Also, in scalar gauge theory, I can not
see how your explaination works, since we got no fermion there.
Actually, I do not know how to answer this question either:), maybe
microsystem can give us a standard answer? :)
Just for fun, the second question comes:
In massless QCD, flavor U(3)L*U(3)R is spontanousely broken to U(3), then |
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x*****d
发帖数: 427 | 23 xy: V --> V
xy(z)=(y.z)x here . means scalar product.
So it's basicly a linear transformation.
If you want a tensor form, that will be x \otimes y*
where y* is the conjugate element of y in V*: y*(z)=y.z |
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T*********r
发帖数: 11175 | 24 Gary Shiu's paper
http://arxiv.org/abs/hep-th/0610151
Using DBI inflation as an example, we demonstrate that the detailed geometry
of warped compactification can leave an imprint on the cosmic microwave
background (CMB). We compute CMB observables for DBI inflation in a generic
class of warped throats and find that the results (such as the sign of the
tilt of the scalar perturbations and its running) depend sensitively on the
precise shape of the warp factor. In particular, we analyze the warped |
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D******n
发帖数: 2836 | 25 a curve doesnt approach any scalar value. a curve is a curve.
it is the AUC(area under the roc curve) should be as close as possible to
one. |
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s*****n
发帖数: 2174 | 26 我补充一点, 用于条件判断的时候, 永远应该用 && 和 || .
条件判断的时候, 需要的总是一个明确的TRUE or FALSE, 从不需要向量.
比如下面这样的code, 在我们公司里面, 就属于不合格的code,
哪怕a和b都是scalar. 如果有人面试中写出这样的code, 基本就
可以认定此人没有经过很好的R的训练.
if (a > 0 & b < 0){
## do something here
}
如果条件是基于一个向量里面所有元素的什么关系, 则用any() 和 all()
比如下面这样的code是允许的.
if (all(vec.a > 0 & vec.b <= 0)){
## do something here
} |
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n******0
发帖数: 298 | 27 i don't think it is necessary. f should be a scalar. |
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n**f
发帖数: 121 | 28 Thank you again for your reply.
g(X) is just standard LogNormal distribution. This part is straightforward.
My challenge is that: X is a scalar and V is a vector. So finding V=f'(x|
theta)
is very difficult -- at least for me. In reality, V is a K-dimensionional
vector that satisfies the following equation:
X = v_1 / sum_{i=1...K-1}{theta_k*v_k}.
One can argue that V is not identifiable with X and theta given. |
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R*******c
发帖数: 249 | 29 y_i is just a scalar.
I know that the model is un-identifiable, but my question is, if I set
vague/diffuse bayes priors for each parameter, what will happen? |
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s**u
发帖数: 383 | 30 经高手指导，compile 没有问题了， 但是initial 又出问题了， 说是NIL
dereference (read)， 查了manual, 说是 'NIL dereference (read)' can occur at
compilation in some circumstances when an inappropriate transformation is
made, for example an array into a scalar.用gen initial也出现同样的error.
请高人指导，谢谢。
model {
for (i in 1:k-1) {
for (j in i+1:k){
win1[i,j] ~ dbin(p[i,j], n)
logit(p[i,j]) <- d[i]-d[j]}
# p[i] <- phi(d[ind1[i]] - d[ind2[i]])
}
d[1:k] ~dmnorm(dmu[ ]... 阅读全帖 |
|
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z****e
发帖数: 702 | 32 对于带参数a的概率密度f(x|a),
在a为scalar的情况，fisher信息也是个标量，这样可以通过求fisher信息最大值的方
法找到a；
但是当a为vector时，fisher信息是个矩阵，这个情况下该怎么求a呢？
最近问题比较多，感谢大家的帮助。thx |
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a**********9
发帖数: 491 | 33 各位大哥大姐，帮帮我吧，被折腾的崩溃了。
我用的正版sas 9.2运行下面proc iml时出现错误：
ERROR: The SAS/IML product with which IML is associated is either not
licensed for your system or the
product license has expired. Please contact your SAS installation
representative.
1 proc iml;*invokes IML;
ERROR: Bad product ID for procedure IML.
2 a = 2; *scalar;
3 b = {1 2 3 4}; *1 x 4 row vector;
4 c = {1.0 0 0, 0.2 1.0 0, 0.8 0.4 1.0}; *3 x 3 (correlation) matrix;
5 quit;
然后我去安装了SAS IML studio 3.4，可是打开总是出现错误
谁能给帮帮忙啊... 阅读全帖 |
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l******9
发帖数: 579 | 34 Thanks,
But, in clustering, each data piont is a scalar (a number).
In my problem, each data piont is a vector that contains a group of numbers.
The distance between two vectors is a the linear correlation of teh two
vectors not two data points in the two vectors.
Example,
v1 = [1, 2, 3]
v2 = [4, 6, 8]
v3 = [10, 5, 9]
v1 and v2 has strong correlation than v1 and v3 or v2 and v3.
So,, v1 and v2 should be put in the same cluster but v3 cannot be.
Any help would be appreciated. |
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h***x
发帖数: 586 | 35 1) As catforfish said, the data point is not necessary to be a scalar, a
vector is fine. All my work on clustering are for multi dimension instead of
one dimension. I suggest you spending some time to learn clustering first.
2)In your example, v1 and v2 has strong correlation. If you want to take
this into account in clustering, you should not use euclidean distance as
the statistical measure, you can use other measures with the features you
like for your task.
3)For clustering, result explanati... 阅读全帖 |
|
l******n
发帖数: 9344 | 36 很多公司都在做类似的东西，有些直接重写interpreter，效率更高
operations
performance
tree |
|
c****t
发帖数: 19049 | 37 现在这词用法混乱。比较多接受的有3个意思:1.documents, graphs,videos,不能直接
放进relational database里。big是说文件做为scalar size大; 2.real-time (simple
) analytics on database着眼点不是你能不能在你的PC上干，而是你只能在data
server/cluster上做。big是说要在“大”机器上做; 3.最常见的混淆，特别是做data
analysis出身的，是说有好多rows,好多columns。那更多是high-performance
computing |
|
d*****r
发帖数: 41 | 38 感觉以一个Nx1的vector对一个scalar function 做gradient，结果应该是一个Nx1的
vector，没道理变成一个1xN的vector啊
3.13的那个transpose可能是不对啊，谁是大牛来说说 |
|
l*****y
发帖数: 5 | 39 I have such type of matrix problems: An unknow matrix X \in R^{nxn} satisfies
an equation with X in quadratic form (power to two). For example, X is real
symmetric and the equation is:
( P * X * P' + Q ) = X * R * (P * X * P' + Q ) + X
P, Q, and R are given constant matrices. My question is: what is the approach
to generally solve such type of equations? it is really a simple quadratic
equation for any scalar X (middle school problem). But how about if X is an
unknown matrix? Is such type of mat |
|
f*******d
发帖数: 339 | 40 译的不太准确， scalar field 应译为标量场， dark energy 一般译为暗能量。
唉， 两年前我就知道这个塌缩的结果， 还和当时的老板讨论过，
不过没想到要深入研究下去写成文章， 因为当时觉得没太大意义，而且以前也有人写过文章。
现在想想亏了， 后来Steinhardt, Ovrut, Turok, Linde 这些大腕往string， Supergravity 上一扯，
硬是把这玩意炒火了。 |
|
