Thursday 5 October 2017

天空为什么是蓝色的(散射)
































天空里有这么多颜色,为什么我平时看到的只有蓝色呢?
    阳光从天空照射下来,会连续不断地碰到某些障碍。有氮气、氧气、气体微粒和微小的漂浮微粒等等。当光线遇到这些障碍的时候,自然也就改变了自己的方向。
    蓝色光和紫色光的波长比较短;而橙色光和红色光的波长比较长。当遇到空气中的障碍物的时候,蓝色光和紫色光因为翻不过去那些障碍,便被“散射”得到处都是,布满整个天空,就是这样被“散射”成了蓝色。
    发现这种“散射”现象的科学家叫瑞利,他是在130年前发现的,他也是诺贝尔奖获得者。



太阳光是由红、橙、黄、绿、青、蓝、紫七种颜色组成的。这七种颜色的光波长是不一样的。大气中的尘埃以及其他微粒散射蓝光的能力大于散射其他波长较长的光子的能力,因此天空显现出蓝色。
大气对光线的散射主要有两种:丁达尔散射和瑞利散射。其中尘埃、水雾等能在空气中形成胶体的微粒对光的散射属于丁达尔散射,丁达尔散射的特点是散射光的强度与光波波长无关,因此白光散射后仍然是白光,在地平线附近看到的白蒙蒙一片就是丁达尔散射现象。?
还有一种是瑞利散射,是由极小微粒(分子、原子等)产生的散射,其散射光强度与光波波长的四次方成反比,已知可见光的波长范围是400nm(蓝紫光)到700nm(红光),红光端波长是蓝紫光波长的1.75倍,因此蓝紫光散射强度接近红光散射强度的十倍,又因为人眼对紫光不太敏感,所我们看到的天空就是蓝色的。


其实太阳光谱中紫色光比蓝色光波长更短,那么为何天空不是紫色的呢?这是因为太阳光中紫光含量较少,而且人眼对紫光不敏感,所以蓝光才起到了主导作用。
而直视太阳时,短波长的光由于都被散射到四面八方,因此进入眼镜的反而是更长波长的黄色光。
但早晨和傍晚我们直视太阳时,由于太阳高度很低,到达我们人眼的太阳光经历了更长的路程,就连黄色的光都被散射了,剩下的则是更长波长的红光,因此看起来太阳呈现红色。
其实瑞利散射能够解释的并不仅仅是天空和太阳的颜色,还是大海的颜色。大海的主要成分是水,而水本身是无色的。不过也由于瑞利散射的存在,进入大海的太阳光内短波长的光被水分子大量散射,进入人眼;而长波长的光则进入了深海中,逐渐被吸收。因此大海呈现的也是蓝色。

http://freebsd5.psjh.cy.edu.tw/~chemphy/complement/4/4-4/4.html








Wednesday 5 July 2017

Saturday 1 July 2017

How Long Does It Take To Ovulate?

How Long Does It Take To Ovulate?



A woman needs to ovulate each menstrual cycle in order to become pregnant. During a healthy menstrual cycle, a series of hormone secretions lead to the maturation of a dominant follicle in the ovary and release of an egg or ovum (ovulation) to meet a sperm for fertilization in the fallopian tube.


For a variety of reasons some women don’t know the events that need to happen for ovulation to occur, or when they ovulate each menstrual cycle, and many others suffer from ovulatory dysfunction or anovulation. Failure to ovulate is one of the primary causes of infertility.


女人需要每个月经周期的排卵才能怀孕。在一个健康的月经周期中,一系列的激素分泌会导致卵巢中一个显性卵泡的成熟,释放一个卵子或卵子(排卵)以满足精子在输卵管内受精的需要。


出于各种原因,一些女性不知道排卵事件,或者不知道几时是排卵期,还有许多人患排卵障碍或不排卵。不排卵是不孕的主要原因。









This video is an informative animated presentation that explains in detail about ovulation.

Ovulation is a part of the menstrual cycle when the ovary releases an egg or ovum.

Inside the ovary there are thousands of follicles. Each follicle is a hollow ball of cell with an immature egg in the center.

The typical 28-day menstrual cycle begins on the first day of the menstrual bleeding.
During the first seven days of the cycle, a few follicles begin to grow at the same time.

These maturing follicles secrete estrogen hormone into the bloodstream to prepare the lining of the uterus for pregnancy.

Around day 7, all of the follicle stop growing and begin to degenerate except for one, this dominant  follicle continues to grow and nourishes the developing egg inside it.

Around day 12, the follicle secretes a large amount of estrogen into the bloodstream.

When the estrogen reaches the hypothalamus in the pituitary gland in the brain, the anterior or the fun part of the pituitary gland releases a huge surge of luteinizing hormone into the bloodstream.

Watch the video to know more in detail about Ovulation.
这个视频是一个内容丰富的动画演示,详细解释关于排卵。

当卵巢释放卵子或卵子时,排卵是月经周期的一部分。

卵巢内有数千个卵泡。每个卵泡都是一个中空的球状细胞,中间有一个未成熟的卵细胞。

典型的28天月经周期开始于月经来潮的第一天。在周期的前七天,一些卵泡同时开始生长。

这些成熟的卵泡分泌雌激素进入血液,为怀孕准备子宫内膜。

大约在第7天,所有的卵泡停止生长并开始退化,除了优势卵泡继续生长并滋养发育中的卵子。

大约在第12天,卵泡分泌大量的雌激素进入血流。

当雌激素到达脑下垂体中的下丘脑时,垂体前部会释放大量黄体生成素进入血流。

观看视频了解更多关于排卵的细节。








ovulation is a part of the menstrual cycle when the ovary releases a ripe egg
or ovum inside the ovary are hundreds of thousands of follicles each follicle is
a hollow ball of cells with an immature egg in the center the typical 28-day menstrual cycle begins on the first day of menstrual bleeding during the first seven days of the cycle a few follicles begin to grow at the same time these maturing follicles secrete estrogen hormone into the bloodstream to prepare the lining of the uterus for pregnancy around day seven all of the follicles stop growing and begin to degenerate except for one this dominant follicle continues to grow and nourishes the developing egg inside it around day 12 the follicle secretes a large amount of estrogen into the bloodstream when the estrogen reaches the hypothalamus and
the pituitary gland in the brain the anterior or front part of the pituitary gland releases a huge surge of luteinizing hormone into the bloodstream around day 14 luteinizing hormone causes
the follicle to undergo a sudden growth spurt right before ovulation the egg detaches from the inside of the follicle the bulging follicle releases chemicals causing one of the two fallopian tubes to move in closer and surround the follicle. the follicle swells until it bursts open ejecting the egg and fluid from the follicle into the abdominal cavity , in response the thin Bri a tiny projections at the end of the fallopian tube sweep across the ovulation site and pick up the egg microscopic cilia on the fem ba surface transport the egg to the entrance of the fallopian tube inside the walls of the fallopian tube muscular contractions gently push the egg towards the uterus after ovulation the egg lives for 12 to 24 hours so it must be fertilized by a sperm from the male during this time for a woman to become pregnant if it's not fertilized the egg dissolves away and is shed along with the uterine lining during menstruation











Thursday 22 June 2017

How menstruation works

How menstruation works


http://ed.ted.com/lessons/how-menstruation-works-emma-bryce


This might seem hard to believe, but right now,
300 million women across the planet are experiencing the same thing:
a period.
The monthly menstrual cycle that leads to the period
is a reality most women on Earth will go through in their lives.
But why is this cycle so universal?
And what makes it a cycle in the first place?
Periods last anywhere between two and seven days,
arising once within in a 28-day rotation.
That whole system occurs on repeat,
happening approximately 450 times during a woman's life.
Behind the scenes are a series of hormonal controls
that fine tune the body's internal workings
to make menstruation start or stop during those 28 days.
This inner machinery includes two ovaries
stocked with thousands of tiny sacks called follicles
that each contain one oocyte, an unfertilized egg cell.
At puberty, ovaries hold over 400 thousand egg cells,
but release only one each month,
which results in pregnancy or a period.
Here's how this cycle unfolds.
Each month beginning around puberty,
the hormone-producing pituitary gland in the brain
starts releasing two substances into the blood:
follicle stimulating hormone and luteinizing hormone.
When they reach the ovaries,
they encourage the internal egg cells to grow and mature.
The follicles respond by pumping out estrogen.
The egg cells grow and estrogen levels peak,
inhibiting the production of FSH,
and telling the pituitary to pump out more LH.
That causes only the most mature egg cell from one of the ovaries
to burst out of the follicle and through the ovary wall.
This is called ovulation,
and it usually happens ten to sixteen days before the start of a period.
The tiny oocyte moves along the fallopian tube.
A pregnancy can only occur if the egg is fertilized by a sperm cell
within the next 24 hours.
Otherwise, the egg's escapade ends,
and the window for pregnancy closes for that month.
Meanwhile, the now empty follicle begins to release progesterone,
another hormone that tells the womb's lining
to plump up with blood and nutrients
in preparation for a fertilized egg that may embed there and grow.
If it doesn't embed,
a few days later, the body's progesterone and estrogen levels plummet,
meaning the womb stops padding out and starts to degenerate,
eventually falling away.
Blood and tissue leave the body, forming the period.
The womb can take up to a week to clear out its unused contents,
after which, the cycle begins anew.
Soon afterwards, the ovaries begin to secrete estrogen again,
and the womb lining thickens,
getting ready to accommodate a fertilized egg
or be shed.
Hormones continually control these activities
by circulating in ideal amounts delivered at just the right time.
The cycle keeps on turning,
transforming each day and each week into a milestone along its course
towards pregnancy or a period.
Although this cycle appears to move by clockwork,
there's room for variation.
Women and their bodies are unique, after all.
Menstrual cycles occur at diffferent times in the month,
ovulation comes at various points in the cycle,
and some periods last longer than others.
Menstruation even begins and ends at different times in life
for different women, too.
In other words, variations between periods are normal.
Appreciating these differences and learning about this monthly process
can empower women,
giving them the tools to understand and take charge of their own bodies.
That way, they're able to factor this small cycle

into a much larger cycle of life.

这听上去令人难以置信,但是现在全球近3亿的女性正在经历着同样的事情:一段特殊的时期。
这就是每月一次的月经期,是一个全球妇女在她们的一生中必然要面对的现实。
但为什么这个周期如此普遍呢?最开始的周期是怎样形成的呢?
月经会持续2-7天,每28天循环发生。
月经现象会重复不断地出现,
女人的一生大概会有450次的月经。

表象之下,这一切都是由人体激素进行调控的,
激素精密地控制着身体内部的运作,
在这28天里控制经期的起始。
这套内部机制包含两个卵巢,卵巢内存有成千上万的微小袋子,叫做卵泡,
每个卵泡内都含有一个卵母细胞,即未受精卵细胞。
青春期时期,卵巢内含有超过40万的卵细胞,
但每个月只会释放出一个卵细胞,
正是这个卵细胞决定着女性是受孕还是月经。
接下来我们来看看这个循环过程是如何产生的。
青春期的每个月初时候,大脑中的脑下垂体会分泌激素
向血液中释放两种物质:促卵泡激素和黄体化激素。
当它们到达卵巢后,会促进子卵巢内卵泡的发育和成熟。
卵泡的成熟,会进一步促进雌性激素的分泌。
伴随着卵细胞的成长,雌性激素的分泌也将达到峰值,
同时抑制促卵泡激素,
促进垂体释放更多的黄体化激素。
结果就是,只有其中一个卵巢中发育最为成熟的卵细胞,
才能冲出卵泡,穿越子房壁。
这就是排卵现象,排卵通常发生在月经前的1016天。
微小的卵母细胞沿输卵管运动。
只有当卵母细胞(卵子)和精子结合后女性才会受孕,
这需要在排卵后24小时之内发生。
否则,意味着卵子使命的终结,女性在该月受孕的窗口也会关闭。
与此同时,空虚的卵泡开始释放孕酮,另一种激素以刺激子宫内膜
产生血液和营养物质,为受精卵的着床和生长做准备。
如果没有受精卵着床,几天后,身体的孕酮和雌性激素骤降,
刺激子宫停止补充养分,内膜开始退化坏死,渐渐脱落。
血液和脱落的子宫内膜离开身体,形成月经。
子宫清理内部无用物质的过程常常会持续一周,
之后,一个新的周期又开始了。
很快,卵巢又开始分泌雌性激素,
子宫内膜开始变厚,为受精卵着床最准备或再一次脱落。
激素长期控制着整个活动过程,通过在精确的时间输送理想的量。
随着周期的循环前行,令每一天,每个星期,
都是这个受孕或经期过程中的一个里程碑。

虽然这个过程看上去如时钟般精准,但它仍然会有区别。
毕竟每位女性及其身体都是独一无二的。
每个月,月经产生的时间因人而异;
排卵期出现的节点不同;甚至经期持续的时间也各有长短。
另外,对于不同的女性来说,一生中初潮和绝经的时间也不尽相同。
换言之,不同个体的经期有差别是正常的。
欣赏这些不同并学习关于生理周期的过程,
能让女性更加的从容,自主,让女性了解并掌控自己的身体。
这样,她们能够将从这个小周期领会到的东西,
运用在更加复杂的生活周期之中。



http://www.mayoclinic.org/healthy-lifestyle/womens-health/in-depth/menstrual-cycle/art-20047186