no idea

Evol Reverof: Chapter 5

nice story from my friend...
LOL

Ways To Improve Your Memory

The human brai­n is like a library that stock­s memories instead of books. In some ways, that makes the hippocampus, the part of the brain most involved in memory, the brain's librarian. The hippocampus has the most responsibility in this cranial library, juggling the new releases of short-term memory while cataloging materials for the permanent collection of long-term memory. It's not the only part at work, however, in storing these chapters of our lives. Different kinds of memory are stored in different areas of the brain. With such a large system, the brain needs a system of encoding and retrieving memories, something a bit more complex than the local library's Dewey Decimal System.

The brain has to be able to pull information at the drop of a hat, whether it's a fact on hold (such as a telephone number) or a dusty memory that's been sitting in storage for years (the memory of your first kiss). No one likes a library that loses books or shelves them in the wrong place. Yet sometimes we find ourselves with a very poor librarian on our hands, one that doesn't allow us to retrieve memories when we need them. Sometimes it's trivial, like when we tear apart our homes looking for glasses perched innocuously atop our heads, and sometimes these lapses in memories are more embarrassing, such as when we call a colleague "sport" because we simply can't remember his name.

Whether you're a college student studying for an important test or an aging baby boomer concerned about forgetting a recent doctor's appointment, there are a few things everyone can do to optimize the storage and checkouts in our private libraries of memories. Alert the librarian and head to the next page for the first tip.

(Q&A) Solve: cos2x+cos4x=0 ?

Q:-

Solve between (0, 2pi): cos2x +cos4x = 0

A:-

0 = cos2x + cos4x = cos2x + 2(cos2x)^2 - 1
because cos2a = cos^2 a - sin^2 a = cos^2 a - (1 - cos^2 a)

Put A=cos2x.
Then from the above:
0 = 2A^2 + A - 1 = (2A - 1)(A + 1)
and this implies
A = -1 or A = 1/2
ie
cos2x = -1 or cos2x = 1/2

cos2x = -1 implies:
2x = pi or 3pi, so x=pi/2 or 3pi/2

cos2x = 1/2 implies:
2x = pi/3 or 5pi/3 or 7pi/3 or 11pi/3
so x=pi/6 or 5pi/6 or 7pi/6 or 11pi/6

So all the solutions are:
pi/6, pi/2, 5pi/6, 7pi/6, 3pi/2, 11pi/6

HDTV

When the first high-definition television (HDTV) sets hit the market in 1998, movie buffs, sports fans and tech aficionados got pretty excited, and for good reason. Ads for the sets hinted at a television paradise with superior resolution and digital surround sound. With HDTV, you could also play movies in their original widescreen format without the letterbox "black bars" that some people find annoying.

But for a lot of people, HDTV hasn't delivered a ready-made source for transcendent experiences in front of the tube. Instead, people have gone shopping for a TV and found themselves surrounded by confusing abbreviations and too many choices. Some have even hooked up their new HDTV sets only to discover that the picture doesn't look good.

Fortunately, a few basic facts easily dispel all of this confusion. In this article, we'll look at the differences between analog, digital and high-definition, explain the acronyms and resolution levels and give you the facts on the United States transition to all-digital television. We'll also tell you exactly what you need to know if you're thinking about upgrading to HDTV.

Analog, Digital and HDTV

For years, watching TV has involved analog signals and cathode ray tube (CRT) sets. The signal is made of continually varying radio waves that the TV translates into a picture and sound. An analog signal can reach a person's TV over the air, through a cable or via satellite. Digital signals, like the ones from DVD players, are converted to analog when played on traditional TVs. (You can read about how the TV interprets the signal in How Television Works.)

This system has worked pretty well for a long time, but it has some limitations:

* Conventional CRT sets display around 480 visible lines of pixels. Broadcasters have been sending signals that work well with this resolution for years, and they can't fit enough resolution to fill a huge television into the analog signal.
* Analog pictures are interlaced -- a CRT's electron gun paints only half the lines for each pass down the screen. On some TVs, interlacing makes the picture flicker.
* Converting video to analog format lowers its quality.

Analog TVs like this one can't use digital signals without a
set-top converter.

United States broadcasting is currently changing to digital television (DTV). A digital signal transmits the information for video and sound as ones and zeros instead of as a wave. For over-the-air broadcasting, DTV will generally use the UHF portion of the radio spectrum with a 6 MHz bandwidth, just like analog TV signals do.

DTV has several advantages:

* The picture, even when displayed on a small TV, is better quality.
* A digital signal can support a higher resolution, so the picture will still look good when shown on a larger TV screen.
* The video can be progressive rather than interlaced -- the screen shows the entire picture for every frame instead of every other line of pixels.
* TV stations can broadcast several signals using the same bandwidth. This is called multicasting.
* If broadcasters choose to, they can include interactive content or additional information with the DTV signal.
* It can support high-definition (HDTV) broadcasts.

DTV also has one really big disadvantage: Analog TVs can't decode and display digital signals. When analog broadcasting ends, you'll only be able to watch TV on your trusty old set if you have cable or satellite service transmitting analog signals or if you have a set-top digital converter.

This brings us to the first big misconception about HDTV. Some people believe that the United States is switching to HDTV -- that all they'll need for HDTV is a new TV and that they'll automatically have HDTV when analog service ends. Unfortunately, none of this is true.

HDTV is just one part of the DTV transition. We'll look at HDTV in more detail, including what makes it different from DTV, in the next section.

DTV vs. HDTV
The Advanced Television Standards Committee (ATSC) has set voluntary standards for digital television. These standards include how sound and video are encoded and transmitted. They also provide guidelines for different levels of quality. All of the digital standards are better in quality than analog signals. HDTV standards are the top tier of all the digital signals.

The ATSC has created 18 commonly used digital broadcast formats for video. The lowest quality digital format is about the same as the highest quality an analog TV can display. The 18 formats cover differences in:

* Aspect ratio - Standard television has a 4:3 aspect ratio -- it is four units wide by three units high. HDTV has a 16:9 aspect ratio, more like a movie screen.
* Resolution - The lowest standard resolution (SDTV) will be about the same as analog TV and will go up to 704 x 480 pixels. The highest HDTV resolution is 1920 x 1080 pixels. HDTV can display about ten times as many pixels as an analog TV set.
* Frame rate - A set's frame rate describes how many times it creates a complete picture on the screen every second. DTV frame rates usually end in "i" or "p" to denote whether they are interlaced or progressive. DTV frame rates range from 24p (24 frames per second, progressive) to 60p (60 frames per second, progressive).

Many of these standards have exactly the same aspect ratio and resolution -- their frame rates differentiate them from one another. When you hear someone mention a "1080i" HDTV set, they're talking about one that has a native resolution of 1920 x 1080 pixels and can display 60 frames per second, interlaced.

Broadcasters get to decide which of these formats they will use and whether they will broadcast in high definition -- many are already using digital and high-definition signals. Electronics manufacturers get to decide which aspect ratios and resolutions their TVs will use. Consumers get to decide which resolutions are most important to them and buy their new equipment based on that.

Until the analog shutoff date, broadcasters will have two available channels to send their signal -- a channel for analog, and a "virtual" channel for digital. Right now, people can watch an over-the-air digital signal only if they are tuned in to the broadcaster's virtual digital channel. After analog broadcasting ends, the only signals people will receive over the air will be digital.

However, even though a digital signal is better quality than an analog signal, it isn't necessarily high definition. HDTV is simply the highest of all the DTV standards. But whether you see a high-definition picture and hear the accompanying Dolby Digital® sound depends on two things. First, the station has to be broadcasting a high-definition signal. Second, you have to have the right equipment to receive and view it. We'll look at how to get an HDTV set and signal next.

(Q&A)I need to calculate volume of C7H16 required to boil 36L of water with 15% efficiency

Q:-
std enthalpy is -224.4 kJ
density is .78g/mol

36,000g * 4.184 * 75 = 11296.8 kJ required to heat the water

which leaves (224.4*.15)x = 11296.8 or x = 335.62 moles of C7H16

335.62 moles * 100 g/mol = 33562 g / .78 = 43027.56 mL of C7H16 required to heat the water...

Except the answer 43027.56 is not right...

Here is the problem:
When backpacking in the wilderness, hikers often boil water to sterilize it for drinking.
Suppose that you are planning a backpacking trip and will need to boil 36 L of water for your group.

What volume of fuel should you bring? Assume each of the following:
the fuel has an average formula of C7H16 ; 15% of the heat generated from combustion goes
to heat the water (the rest is lost to the surroundings);
the density of the fuel is 0.78 g/mL; the initial temperature
of the water is 25.0C; and the standard enthalpy of
formation of C7H16 is -224.4 kJ/mol..

i'm still missing something subtle... I come out to 43000 mL of C7H16 each time....

A:-
Your problem is the you supplied the dHf of heptane and NOT the heat of combustion!

-224.4 kJ/mole vs -44.566MJ/kg is a BIG difference.
I thought 224 kJ for combustion was small but did not check it out earlier.

Let UNITs guide you; always USE THEM in your calculation to prevent errors

Firstly, the eqn: C7H16 + 11O2 -----> 7CO2 + 8H2O + heat

dH comb/ mole C7H16 = 44.566 MJ /kg C7H16 = 44.566 kJ/g

dH comb J /ml C7H16 = 44.566kJ/ g * 0.78 g/ml = ?? 34.76 kJ/ml

heat needed, if 100% eff = 36000 g * 4.184 J/gC * 75 C = ??
11.3 MJ

if 15% eff then heat needed = 100% eff/15% * heat needed if 100% = 75.3 MJ

vol of C7H16 needed = heat needed / (+dH comb / ml C7H16) = 75.3 MJ / 34.76 kJ/ml ?? 2167 ml

liters C7H16 needed = vol ml / 1000ml/liter = ?? 2.17 liters

1 liter = 0.26 US gal; so 2.17 liters * 0.26 gal/liter = 0.56 gal

Plug and SOLVE

Basic mathematics is a prerequisite to chemistry – I just try to help you with the methodology of solving the problem.

My life~!!

My exam ends alreadi...
i wanna go out...
but, even i'm freed...
my sis gonna have exam, my 1st bro busy working, my 2nd bro is the exam b4 graduate...
my father and mother busy.. only saturday and sunday got time...

2 days back..
my mother invite me to go to sunway pyramids..
becoz my father got public mutual ceremony...
by that time, my mom and my sis go to sunway pyramid..
i said i don wan go... becoz..
me go with my mother and my sis??
i more like to go with my father..
becoz me and him got same interest...
furthermore, i don wan meet any of my friend there when i'm walking with my mom and sis...
my dad said it is better me stay at home,
becoz got someone come to repair my gate...
i watch tv...
at last, when they back home...
i ask hows shopping?

my mother said "when we were at the sunway, my dad call to invite my mom to the ceremony, the its okay la and the ceremony was great"
my sis said "we just decided to go to so much place there... the ceremony is for the person that wanna pencen... so boring.. but the cakes was delicious..."

fortunately, i didnt go..
kwahah~!! ^^
i can watch my favorite story..
happy sunday (kbs world)

Thrust SSC (SuperSonic Car)

Thrust SSC (SuperSonic Car) is a British-designed and built jet-propelled car developed by Richard Noble, Glynne Bowsher, Ron Ayers and Jeremy Bliss.[1]
ThrustSSC.
ThrustSSC.

ThrustSSC holds the World Land Speed Record, set on October 15, 1997, when it achieved a speed of 1,228 km/h (763 mph) and became the first land vehicle to officially break the sound barrier, not considering the earlier, unsubstantiated claim of the Budweiser Rocket.

The car was driven by Royal Air Force fighter pilot Squadron Leader Andy Green in the Black Rock Desert in Nevada, United States. It was powered by two afterburning Rolls-Royce Spey turbofan engines, as used in British F-4 Phantom II jet fighters. It is 16.5 m (54 ft) long, 3.7 m (12 ft) wide and weighs 10.5 tons (10.7 t). The twin engines developed a thrust of 223 kN (50,000 lbf) and burned around 4 Imperial gallons per second (18.2 l/s or 4.8 US gallons/s). Transformed into the usual terms for car mileages based on its maximum speed, the fuel consumption was about 5,500 l/100 km or 0.04 mpg U.S.

After the record was set, the World Motor Sport Council released the following message:

The World Motor Sport Council homologated the new world land speed records set by the team ThrustSSC of Richard Noble, driver Andy Green, on 15 October 1997 at Black Rock Desert, Nevada (USA). This is the first time in history that a land vehicle has exceeded the speed of sound. The new records are as follows:

* Flying mile 1227.986 km/h (763.035 mph)
* Flying kilometre 1223.657 km/h (760.343 mph)

In setting the record, the sound barrier was broken in both the north and south runs.

In 1983 Richard Noble had broken the world land speed record with his earlier car Thrust2, which reached a speed of 1,018 km/h (633 mph). Both ThrustSSC and Thrust2 are displayed at the Coventry Transport Museum in Coventry, England.

The date of Andy Green's record came exactly a half century and one day after Chuck Yeager broke the sound barrier in Earth's atmosphere, with the Bell X-1 research rocket plane on October 14, 1947.

Several teams are competing to break the record, for example the North American Eagle project.

(Q&A) Equations

Q:-
C5H8O2 + CoCl2.6H2O --> Co(C5H8O2)3 + Cl2 + H2O

A:-
3C5H8O2 + CoCl2 * 6H2O ► Co(C5H8O2)3 + Cl2 + 6H2O

(Q&A) How many aspirin tablets could be made from 4g of salicylic acid?

Q:-
A regular dose of aspirin contains 325 mg of aspirin. How many aspirin tablets could be made from the aspirin prepared when 4g of salicylic acid was used with excess amount of acetic anhydride?

A:-
after balance equations they are one to one ratio so:

4g (C7H6O3) x 1mol salicylic acid (s.a)/138.07g s.a. x 1mol aspirin (as)/ 1 mol s.a x 180.07g as/ 1 mol as = 5.2174g of aspiring.
now divide the theorical yield over the regular dose of aspiring in a tablet, (dont forget to convert milligrams to grams) so: 5.2174g/0.325g= 16.0 tablets

Active~!!

At last..
after i waited for more than 60+ days...
it already ends...
i felt very happy...
right now,
i can celebrate the day...
but b4 this,
my family always say to me go study, study after this, study, study, study....
right now,
go do see why the pump not working, go clean the pond, go water the plant, go buy things at shop...
kwahaha~!!