多个个星云的融合点形成超大质量黑洞，产生强辐射，照量整个星空。
好几个这样的地方被Swift卫星的硬X射线照相机照下来了。
Swift-detected active black holes in merging galaxies
详细解释见此。
对我而言多了解一下宇宙的生成变化就不会怕死，甚至觉得死了比较好。
这个就是黑洞
Monthly Archives: May 2010
The concept of polymer physics is blurred
Vicki Cleave arranged a virtual issue of the Journal of Polymer Science, Part B: Polymer Physics on Materials View website. All articles in this issue are selected from other journals on Wiley InterScience, in order to demonstrate how wide and interesting the content of modern polymer physics research can be.
The increase of impact factor of J. Polym. Sci., Part B has been lagging behind its sister Part A. 10 years ago, the two journals have close IFs, 1.7 for Part A and 1.2 for Part B. Their 2008 records become 3.8 and 1.5, respectively. Somewhat coincidently, RSC launched a new journal Polymer Chemistry this year, wherears there has been no new journal for polymer physics. These are some loose evidence of the declining of polymer physics research I have long felt about.
However, the virtual issue of Part B tried to tell us there were still high impact polymer physic research that happened to appear on other journals. It now suggests what are also research of polymer physics welcomes future submission from these fields. These areas of research, as indicated by the virtual issue, are:
- Biopolymers
- Photo-, electro- and/or magneto-active polymers and their devices
- Block copolymers (new only if they contain metals or are present on interfaces)
However, what physics is being extracted from these research areas? What problems of physics are still unanswered? And what models are proposed? Is there something similar to mean-field theory by P. Flory or the scaling theory by de Gennes going on? Or at least something similar to what Rouse & Zimm and Doi & Edward did?
The research on biopolymers can now follow a physic aspect only because the research of physics itself is penetrating biology. Little or no that was originally old polymer physics is applicable to biopolymers.
Photo-, electro- and/or magneto-active polymers are interesting because they are promising of soft devices. But ironically the design of them suffers much from their softness, which involves structural and dynamic heterogeniety at multiple timescale as well as nonequilibrium nature.
Block copolymer once attracted physicists after the control of polymer archetacture became easy thanks to controlled polymerization techniques such as ATRP and RAFT. However, now the research is largely simulations rather than theories.
So if Part B considers accepting papers of these research, it can boost its IF to some extent, but the cost is further blurring the concept of “polymer physics”.
为什么G''是负值？
主题回归到流变学一下。
众所周知（线性）粘弹性是处于Hookian弹性和Newtonian粘性这两个极端之间的性质。对Hookian弹性体（Hookian弹簧模型）施加正弦形变，测到的是同相的正弦应力；向Newtonian粘流体（Newtonian粘壶）施加正弦形变速率，测到的是同相的正弦应力。向一个线性粘弹性样品施加正弦形变，测到的是相位角为[eq]\delta[/eq]的正弦应力：[eq]\gamma_0 \sin \left ( \omega t+\delta \right )[/eq]。
小幅振荡力学响应
最为人熟悉的流变学测试（也是最多不懂流变的人知道要做的测试）就是[eq]G'[/eq]、[eq]G”[/eq]~[eq]\omega[/eq]曲线，这个也叫做“粘弹谱”。我曾经详细解释过[eq]G'[/eq]和[eq]G”[/eq]到底是怎么来的。典型线型聚合物粘弹谱如下图：
线型聚合物粘弹谱
下图是我配制的合成锂藻土Laponite凝胶的粘弹谱，发现[eq]G”[/eq]在高频处出现负值。下面是对这个不正常现象的解释。
Laponite凝胶粘弹谱
一台应变控制型流变仪若要给出这样的图，就要给样品施加一定频率[eq]\omega[/eq]和幅度[eq]\gamma[/eq]的正弦应变[eq]\gamma \left ( t \right ) = \gamma_0 \sin \left ( \omega t \right)[/eq]，然后夹具所连接的力学传感器记录样品向夹具施加的转矩，并根据夹具形状和Gap值换算成应变[eq]\sigma \left ( t \right )[/eq]，在线性粘弹性条件下[eq]\sigma \left ( t \right )=\sigma_0 \sin \left ( \omega t + \delta \right )[/eq]。仪品仅需且必须准确测量出两个值：[eq]\sigma_0[/eq]（从在转矩数据中找到的最值换算）和[eq]\delta[/eq]（通过比较转矩数据和应变数据的相位差[eq]\Delta t[/eq]换算，见第1幅图）。其中，[eq]\Delta t=\frac{\delta}{\omega}[/eq]。其他诸如[eq]G'[/eq]、[eq]\eta'[/eq]之类的，都是从这两个数据算出来的。例如[eq]G”=\frac {\sigma_0}{\gamma_0} \sin \left( \omega \right )[/eq]。
如果样品非常接近Hookian弹性体，应力和应变的时间曲线接近同相，相位角[eq]\delta[/eq]的值是非常小的，如果同时频率[eq]\omega[/eq]的值很大，那么相位差[eq]\Delta t[/eq]的值就会非常小。按照第一幅图的情况，，这么大的时间差就算人也能测得很准。但是，在Laponite凝胶粘弹谱中，样品在高频区非常接近Hookian行为，[eq]\delta[/eq]小于2°，这时，如果要求仪器仍然把[eq]\delta[/eq]测准，就等于要求准确分辨小于万分之几秒的时间差。以
为例：
！
仪器是通过比较应力和应变两条曲线在横轴上的位值差来获得[eq]\Delta t[/eq]的。理论上[eq]\Delta t[/eq]再小也总大于0。但如果待测值小于仪器误差，仪器可能就搞不清两条曲线谁前谁后了，就会出现负值的[eq]\Delta t[/eq]，从而出现负值的[eq]\delta[/eq]。虽然[eq]\delta[/eq]出现负值，但绝对值总之并不会太大，所以[eq]\delta[/eq]在第四象限，[eq]\cos\left(\delta\right)\gg 0,\sin\left(\delta\right)<0[/eq]，所以“遭殃”的就会是[eq]G''[/eq]。
总之，[eq]G”<0[/eq]的实质是，Hookian样品损耗角[eq]\delta[/eq]的高频值已超过仪器的测量能力，测出来的值不管是正是负，都在误差范围内，已经不可靠了。