no_tag - sudhang on Diigo

25 Dec 08

HOWTO: Be more productive (Aaron Swartz's Raw Thought)

www.aaronsw.com/...productivity - Preview

time is "fungible" -- that time spent watching TV can just as easily be spent writing a novel. And sadly, that's just not the case.
Time has various levels of quality.
38 more annotations...
- try to make your time higher-quality
- make the best of each kind of time
- Choose good problems
- Is there something more important you can work on?
- Have a bunch of them
- Having a lot of different projects gives you work for different qualities of time
- Make a list
- organize it by kind
- Integrate the list with your life
- Obviously if you attend one of these, you should stop
- Carry pen and paper
- Avoid being interrupted
- You don't want to overdo it. Sometimes if you're really wasting time you should be distracted.
- Eat, sleep, exercise
- Talk to cheerful people
- Share the load
- ust working on a hard problem with someone else makes it much easier
- Procrastination and the mental force field
- So what causes the mental force field? There appear to be two major factors: whether the task is hard and whether it's assigned.
- A task is a specific concrete step you can take towards your goal.
- Simplify it
- The important thing is to have something done right away
- easier to improve something that already exists than to work at a blank page
- Think about it
- inspiration
- how other people did things
- smaller problems
- Assigned problems
- External incentives, like rewards and punishments, kills what psychologists call your "intrinsic motivation" -- your natural interest in the problem.
- it even happens when you try to tell yourself what to do!
- Create a false assignment
- The task has to both seem important (you have to do this to graduate!) and big (hundreds of pages of your best work!) but not actually be so important that putting it off is going to be a disaster.
- Don't assign problems to yourself
- counterproductive
- Make things fun
- So the secret to getting yourself to do something is not to convince yourself you have to do it, but to convince yourself that it's fun. And if it isn't, then you need to make it fun.
- Another way to make things more fun is to solve the meta-problem.
- identify that component (bring it into awareness), and decide the best way to proceed with it.

24 Dec 08

IEEE Spectrum: How We Found the Missing Memristor

www.spectrum.ieee.org/7024 - Preview

had been theorized
nearly 40 years ago,
In the end, memristors might even become the
cornerstone of new analog circuits that compute using an
architecture much like that of the brain.
40 more annotations...
- A memristor is a two-terminal device whose
  resistance depends on the magnitude and polarity of the
  voltage applied to it and the length of time that
  voltage has been applied.
- remembers its most recent resistance until
  the next time you turn it on
- memristor can be used as
  a nonvolatile memory.
- memristors could let us emulate,
  instead of merely simulate, networks of neurons and
  synapses.
- Memristors can be made extremely small
- It turns out that the influence of
  memristance obeys an inverse square law: memristance is
  a million times as important at the nanometer scale as
  it is at the micrometer scale, and it’s essentially
  unobservable at the millimeter scale and larger.
- The crossbar is an array of perpendicular wires.
  Anywhere two wires cross, they are connected by a
  switch. To connect a horizontal wire to a vertical wire
  at any point on the grid, you must close the switch
  between them. Our idea was to open and close these
  switches by applying voltages to the ends of the wires.
- crossbar architecture builds in redundancy by allowing
  you to route around any parts of the circuit that don’t
  work.
- One of the major impediments for prior crossbar memory
  research was the small off-to-on resistance ratio of the
  switches (40 years of research had never produced
  anything surpassing a factor of 2 or 3).
- We found the answer in scanning tunneling microscopy
  (STM)
- We needed some similar mechanism by which we could
  change the effective spacing between two wires in our
  crossbar by 0.3 nm.
- Two platinum
  electrodes (the intersecting wires of the crossbar
  junction) functioned as the “bread” on either end of the
  device
- bottom platinum
  wire to make an extremely thin layer of platinum
  dioxide, which is highly conducting
- film, only one molecule thick, of specially
  designed switching molecules. Over this “monolayer”
- titanium metal, which
  bonds strongly to the molecules and was intended to glue
  them together.
- molecules were supposed to be the actual switches.
  We built an enormous number of these devices,
  experimenting with a wide variety of exotic molecules
  and configurations
- But our fantastic results were inconsistent. Worse yet,
  the success or failure of a device never seemed to
  depend on the same thing.
- Chua had included a graph that looked
  suspiciously similar to the experimental data we were collecting.
- The graph described the current-voltage (I-V)
  characteristics that Chua had plotted for his memristor.
  Chua had called them “pinched-hysteresis loops”; we
  called our I-V characteristics “bow ties.”
- The loop in the I-V curve
  is called hysteresis, and this behavior is startlingly
  similar to how synapses operate: synaptic connections
  between neurons can be made stronger or weaker depending
  on the polarity, strength, and length of a chemical or
  electrical signal.
- What we had
  was not what we had built.
- Under the molecular
  layer, instead of platinum dioxide, there was only pure
  platinum. Above the molecular layer, instead of
  titanium, we found an unexpected and unusual layer of
  titanium dioxide. The titanium had sucked the oxygen
  right out of the platinum dioxide!
- But closer to
  the top platinum electrode, the titanium dioxide was
  missing a tiny amount of its oxygen, between 2 and 3
  percent. We called this oxygen-deficient titanium
  dioxide TiO_2-x, where x is about 0.05.
- Because of this misunderstanding, we had been
  performing the experiment backward.
- molecule monolayer in the middle of our
  sandwich had nothing to do with the actual switching.
  Instead, what it did was control the flow of oxygen from
  the platinum dioxide into the titanium to produce the
  fairly uniform layers of TiO₂ and
  TiO_2-x.
- If a positive voltage is applied to the top
  electrode of the device, it will repel the (also
  positive) oxygen vacancies in the
  TiO_2-x layer down into the pure
  TiO₂ layer. That turns the
  TiO₂ layer into
  TiO_2-x and makes it conductive,
  thus turning the device on. A negative voltage has the
  opposite effect: the vacancies are attracted upward and
  back out of the TiO₂, and thus
  the thickness of the TiO₂ layer
  increases and the device turns off.
- Memristance arises in a semiconductor when both
  electrons and charged dopants are forced to move
  simultaneously by applying a voltage to the system.
- take the molecule
  monolayers out of our devices
- We needed to find the exact
  amounts of titanium and oxygen to get the two layers to
  do their respective jobs.
- The resistance of these
  devices stayed constant whether we turned off the
  voltage or just read their states (interrogating them
  with a voltage so small it left the resistance
  unchanged).
- In its
  initial state, a crossbar memory has only open switches,
  and no information is stored. But once you start closing
  switches, you can store vast amounts of information
  compactly and efficiently. Because memristors remember
  their state, they can store data indefinitely,
- the wires and switches
  can be made very small: we should eventually get down to
  a width of around 4 nm, and then multiple crossbars
  could be stacked on top of each other to create a
  ridiculously high density of stored bits.
- memristors will never eliminate the
  need for transistors: passive devices and circuits
  require active devices like transistors to supply
  energy.
- Chua’s general memristance definition
- how the
  memristor’s voltage depends on current and a “state
  variable”
- In Williams’s memristor, the state
  variable is the thickness of the stoichiometric
  titanium dioxide in the switch; increasing or
  decreasing that thickness causes the device’s
  resistance to increase or decrease.
- changing
  state variable (the TiO₂’s
  thickness) depends on the amount of charge flowing
  through the device.
- Any two crossing wires are connected by a switch
- A positive voltage on the switch
  repels the (positive) oxygen deficiencies in the
  metallic upper TiO_2-x layer,
  sending them into the insulating
  TiO₂ layer below. That causes
  the boundary between the two materials to move down,
  increasing the percentage of conducting
  TiO_2-x and thus the
  conductivity of the entire switch.
- when the voltage is turned off, positive or
  negative, the oxygen bubbles do not migrate. They
  stay where they are, which means that the boundary
  between the two titanium dioxide layers is frozen.
  That is how the memristor “remembers” how much
  voltage was last applied.

IEEE Spectrum: Multicore Is Bad News For Supercomputers

www.spectrum.ieee.org/6912 - Preview

For informatics, more cores doesn’t mean better
performance
At the heart of the trouble is the so-called memory
wall—the growing disparity between how fast a CPU can
operate on data and how fast it can get the data it
needs.
1 more annotations...
- In informatics
  applications, the problem is worse, explains Richard C.
  Murphy, a senior member of the technical staff at
  Sandia, because there is no physical relationship
  between what a processor may be working on and where the
  next set of data it needs may reside.

22 Dec 08

The Future of Photography - TIME

www.time.com/...0,8599,1867320,00.html - Preview

The days of darkrooms and negatives are mostly behind us
film photography lives on in the fine art world
6 more annotations...
- digital photography as a natural evolution of the form
- The photograph becomes the initial research, an image draft, as vulnerable to modification as it has always been to recontextualization
- [A]mateurs increasingly cover the news more effectively than professionals,
- time for professionals to pay more attention to how amateurs envision the world
- circulating within our bodies
  - okayyyyyyyyy :s - on 2008-12-22
  Add Sticky Note
- As each day passes, our view gets richer and more sophisticated thanks to digital technologies

21 Dec 08

Paxos - Pinewiki

pine.cs.yale.edu/Paxos - Preview

one of the most efficient practical algorithms for achieving consensus in a message-passing system with FailureDetectors
Processes are classified as proposers, accepters, and learners
7 more annotations...
- algorithm
- So for each proposal, the algorithm proceeds as follows:
  The proposer sends a message prepare(n) to all accepters. (Sending to only a majority of the accepters is enough, assuming they will all respond.)
  Each accepter compares n to the highest-numbered proposal for which it has responded to a prepare message. If n is greater, it responds with ack(n, v, n_v) where v is the highest-numbered proposal it has accepted and n_v is the number of that proposal (or ⊥, 0 if there is no such proposal). (An optimization at this point is to allow the accepter to send back nack(higher number) to let the proposer know that it's doomed and should back off and try again—this keeps a confused proposer who thinks it's the future from locking up the protocol until 2037.)
  The proposer waits (possibly forever) to receive ack from a majority of accepters. If any ack contained a value, it sets v to the most recent (in proposal number ordering) value that it received. It then sends accept(n, v) to all accepters (or just a majority). You should think of accept as a command ("Accept!") rather than acquiescence ("I accept")—the accepters still need to choose whether to accept or not.
  Upon receiving accept(n, v), an accepter accepts v unless it has already received prepare(n') for some n' > n. If a majority of acceptors accept the value of a given proposal, that value becomes the decision value of the protocol.
- prepare(n)
- accepter compares n to the highest-numbered proposal for which it has responded to a prepare message
- proposer waits (possibly forever) to receive ack from a majority of accepters
- ack contained a value, it sets v to the most recent (in proposal number ordering) value that it received. It then sends accept(n, v) to all accepters (or just a majority).
- Upon receiving accept(n, v), an accepter accepts v unless it has already received prepare(n') for some n' > n. If a majority of acceptors accept the value of a given proposal, that value becomes the decision value of the protocol.

Ars Technica Guide to Virtualization: Part I: Page 3

arstechnica.com/...3 - Preview

the software presents a carefully crafted and controlled model of the whole computer—called a virtual machine—to each guest OS.
5 more annotations...
- three primary types of virtualization, each of which is distinguished by the manner in which the VMM interposes itself in between the hardware and the guest OS:
  
  Emulation (including binary translation)
  Classical virtualization
  Paravirtualization
- software-based model of the entire computer, including the microprocessor. All of the instructions in the instruction streams of both the guest OS and application programs must first pass through the VMM before being passed on to the processor, often so that they can be translated into the processor's native ISA and executed.
- forgo the costly binary translation step and pass the OS and application instruction streams directly on to the processor. The result is that each guest OS and its attendant applications run faster than they would under emulation, but not quite as fast as they would if the OS had exclusive control of the hardware.
- processor traps instructions that might accidentally clue the OS in to the fact that there's something odd and unexpected going on behind its back.
- modifying the guest OS so that these instructions don't pose a problem. With a cooperative guest OS that has been properly modified, the VMM can trust the OS to run with less oversight—and less costly overhead.

Ars Technica Guide to Virtualization: Part I: Page 2

arstechnica.com/...2 - Preview

There are two main ways that this is accomplished: 1) by running a VMM on top of a host OS, and letting it host multiple virtual machines, or 2) by wedging the VMM between the hardware and the guest OSes, in which case the VMM is called a hypervisor.
These guest operating systems don't "know" that they're running on top of another software layer. Each one believes that it has the kind of exclusive and privileged access to the hardware that it needs in order to carry out its isolation and arbitration duties. Much of the challenge of virtualization on an x86 platform lies in maintaining this illusion of supreme privilege for each guest OS.
12 more annotations...
- the hypervisor (also called the virtual machine monitor, or VMM) presents to guest OS a software-created image or simulation of an idealized computer
- called virtual machines (VMs), and the VM is what the OS runs on top of and interacts with.
- as part of a user-level process on a regular OS
- slower than the hypervisor-based approach, since there's much more software sitting between the guest OS and the actual hardware.
- relatively painless to deploy, since you can install them and run them like any other application, without requiring a reboot.
- Server consolidation involves the use of virtualization to replace multiple real but underutilized machines with multiple virtual machines running on a single system.
- saves on space, power, cooling, and maintenance costs.
- live migration, in which an entire virtual machine that's running an OS and application stack is seamlessly moved from one physical server to another, all without any apparent interruption in the OS/application stack's execution.
- By implementing a more robust and coarse-grained form of hardware sharing that swaps entire OS/application stacks on and off the hardware, a VMM can more effectively isolate users and applications from one another for both performance and security reasons.
- Both the Xbox 360 and the Playstation 3 use virtual machines to limit the kinds of software that can be run on the console hardware and to control users' access to protected content
- to write programs for one OS or ISA on another.
- emulation of obsolete hardware, especially older game consoles.

19 Dec 08

The Texas Tech Tornado Cluster

www.acm.org/...tornado.html - Preview

About
$1,300
was
spent
on
the
cluster
during
this
period
primarily
on
network
cards
and
hard
drives.
The
emphasis
through
out
the
construction
of
the
Linux
cluster
was
on
low
cost.
For
teaching
parallel
programming
it¹s
more
important
t
o
first
have
numbers
in
terms
of
cluster
nodes
than
speed
(although
speed
should
not
be
ignored).
Without
numbers,
the
opportunities
to
study
and
learn
about
the
behavior
of
a
multi-computer
cluster
diminishes.

14 Dec 08

Ars Technica Guide to Virtualization: Part I: Page 1

arstechnica.com/...virtualization-guide-1.ars - Preview

"Vanderpool" that was aimed at providing hardware-level support for something called "virtualization."
Virtualization implementations are so widespread that some are even popular in the consumer market, and some (the really popular ones) even involve gaming.
2 more annotations...
- The first of these shifts was the instruction set architecture (ISA) revolution, which was kicked off by IBM's invention of the microcode engine.
- the benefits have less to do with reducing development costs and increasing raw performance than they do with reducing infrastructure costs by allowing software to take better advantage of existing hardware.

29 Nov 08

Natasha Demkina - The Girl with Normal Eyes

www.csicop.org/...demkina.html - Preview

We wanted a test that would prevent Natasha from making diagnoses that could not be disproved
required Natasha to find already established medical abnormalities in the test subjects
3 more annotations...
- Natasha claims to see through people's clothing, yet she says she cannot see through a fabric screen
- Natasha protested during the test that appendixes can grow back after an appendectomy. When told this isn't possible, she insisted that they do grow back in Russia
- Nevertheless, Natasha and her supporters claim she sees what doctors and their tests often miss. The only way I could prove her wrong would be to submit to an autopsy-which I'm not quite ready to do.

09 Nov 08

How To Become A Hacker

www.catb.org/...hacker-howto.html - Preview

There is a community, a shared culture, of expert programmers and
networking wizards
some claim that the hacker
nature is really independent of the particular medium the hacker works
in
10 more annotations...
- The basic difference is this: hackers build things, crackers
  break them.
- get a basic thrill from solving
  problems, sharpening your skills, and exercising your
  intelligence.
- develop a kind of faith in your own learning
  capacity — a belief that even though you may not know all of what you
  need to solve a problem, if you tackle just a piece of it and learn
  from that, you'll learn enough to solve the next piece — and so on,
  until you're done
- automate away the boring bits as much as possible
- exception to this. Hackers will
  sometimes do things that may seem repetitive or boring to an observer
  as a mind-clearing exercise, or in order to acquire a skill or have
  some particular kind of experience you can't have otherwise. But this
  is by choice
- So to behave
  like a hacker, you have to develop an instinctive hostility to
  censorship, secrecy, and the use of force or deception to compel
  responsible adults.
- But
  copping an attitude alone won't make you a hacker, any more than it
  will make you a champion athlete or a rock star. Becoming a hacker
  will take intelligence, practice, dedication, and hard work.
- LISP is worth learning for a different reason — the
  profound enlightenment experience you will have when you finally get
  it. That experience will make you a better programmer for the rest of
  your days, even if you never actually use LISP itself a lot. (You can
  get some beginning experience with LISP fairly easily by writing and
  modifying editing modes for the Emacs text editor, or Script-Fu
  plugins for the GIMP.)
- What will do it is (a) reading code and (b)
  writing code.
- If
  you don't know how to program, writing HTML will teach you some
  mental habits that will help you learn. So build a home page.
  Try to stick to XHTML, which is a cleaner language than classic HTML.

05 Nov 08

Distance-vector routing protocol - Wikipedia, the free encyclopedia

en.wikipedia.org/...stance-vector_routing_protocol - Preview

A distance-vector routing protocol uses the Bellman-Ford algorithm to calculate paths.
DV protocol is based on calculating the direction and distance to any link in a network
2 more annotations...
- Updates are performed periodically in a distance-vector protocol where all or part of a router's routing table is sent to all its neighbors that are configured to use the same distance-vector routing protocol.
- Once a router has this information it is able to amend its own routing table to reflect the changes and then inform its neighbors of the changes

30 Oct 08

Selective Repeat Protocol

www.eas.asu.edu/...gupta5463.html - Preview

If the sequence
number is within the sender's window ,sender sends the packets.
ACK
is received and the packet's sequence number
is equal to base of the sender window, the window moves forward

29 Oct 08

Unqualified Reservations: A straightforward explanation of the present financial crisis (part 1)

unqualified-reservations.blogspot.com/...rd-explanation-of-present.html - Preview

the monetary token in Nitropia is the cowrie.
closed-loop financial system
6 more annotations...
- frictionless market
- formal promises
- ticket
- choke
- The cause of the crisis is a pernicious bit of financial engineering called term transformation.
- ticket so that there are only three variables: the term to maturity, the quantity of cowries to deliver, and the identity of the ticketwriter.

19 Oct 08

Three Way Handshake

www.pccitizen.com/threewayhandshake.htm - Preview

The originator
(you, hopefully) sends an initial
packet called a "SYN" to establish communication and "synchronize" sequence
numbers in counting bytes of data which will be exchanged.

05 Oct 08

Constraint Guide - Binarization

kti.ms.mff.cuni.cz/...binary.html - Preview

Most algorithms of constraint satisfaction restrict to the CSPs in which
each constraint is either unary or binary. Such CSP is usually referred as a binary
CSP.
a binary CSP can be depicted by a constraint graph (sometimes
referred as a constraint network),
in which each node represents a variable, and each arc represents a constraint between variables represented by
the end points of the arc
5 more annotations...
- Because it is possible to convert any CSP with n-ary constraints to another
  equivalent binary CSP, the restriction to binary CSPs is not limitative at all.
- This newly introduced
  variable, we call it an encapsulated variable,
  has assigned a domain that is a Cartesian product of the domains of individual variables.
- Briefly
  speaking, n-ary constraint can be substituted by an encapsulated variable with the domain corresponding to the
  constraint.
- this transformation solves individual constraints
- how to bind
  the encapsulated variables

Constraint Guide - Constraint Satisfaction

kti.ms.mff.cuni.cz/...constrsat.html - Preview

A solution to a CSP is
an assignment of a value from its domain to every variable, in such a
way that every constraint is satisfied
3 more annotations...
- Solutions to CSPs can be found
  by searching systematically through the possible assignments of
  values to variables. Search methods divide into two broad classes,
  those that traverse the space of partial solutions (or partial value
  assignments), and those that explore the space of complete value
  assignments (to all variables) stochastically.
- closer to the original
  problem
- they can sometimes find
  solution more quickly

PsyBlog: How to Improve Your Self-Control

www.spring.org.uk/...-improve-your-self-control.php - Preview

One of humanity's most useful skills, without which advanced civilisations would not exist, is being able to engage our higher cognitive functions, our self-control, to resist these temptations.
Psychologists have found that self-control is strongly associated with what we label success: higher self-esteem, better interpersonal skills, better emotional responses and, perhaps surprisingly, few drawbacks at even very high levels of self-control
7 more annotations...
- Dr Fujita and colleagues have proposed that abstract thinking and psychological distance are particularly important in self-control
- They needed participants to be thinking in either a high-level way (abstract - seeing the whole forest) or a low-level way (concrete - seeing individual trees).
- psychological distance
- people find it much easier to make decisions that demonstrate self-control when they are thinking about events that are distant in time
- Global processing. This means trying to focus on the wood rather than the trees
- Abstract reasoning. This means trying to avoid considering the specific details of the situation at hand in favour of thinking about how actions fit into an overall framework - being philosophical.
- High-level categorisation. This means thinking about high-level concepts rather than specific instances.

Constraint Guide - Introduction

kti.ms.mff.cuni.cz/...intro.html - Preview

declarative
declarative
13 more annotations...
- declarative
- declarative
- declarative
  description and effective solving
- A constraint is simply a logical relation among several unknowns (or variables), each taking a value in a given
  domain. A constraint thus restricts the possible values that variables can take, it represents some partial information
  about the variables of interest.
- partial
- non-directional
- declarative
- declarative
- additive
- rarely independent
- The Constraint Satisfaction Problem (CSP) is a problem where one is given:
  
  a finite set of variables,
  
  a function which maps every variable to a finite domain,
  
  a finite set of constraints.
  
  Each constraint restricts the combination of values that a set of variables
  may take simultaneously. A solution of a CSP is an assignment to each variable a value from its domain satisfying
  all the constraints.
- generate and test
- variables with infinite domains

01 Oct 08

Classic.Ars: Understanding Moore's Law: Page 6

arstechnica.com/...6 - Preview

"power wall" mentioned above. Power
densities cannot keep increasing indefinitely. At some point, active cooling
will be required for all new CPU designs if architects continue on their present
course of adding more and more functionality to a single die.
But one of the
shifts that has already started to happen is that systems vendors are opting to
exploit Moore's Law not by adding more functionality to each chip but by making
smaller chips that can be ganged together via board-level and network-level
integration.
4 more annotations...
- distributed computing paradigm represents an
  alternative way to exploit Moore's Law
- but there is as of yet no "killer
  app" on the horizon that absolutely demands the latest P4
- challenge
  associated with mixing vastly different types of circuits on a single die
- The types of circuits that
  implement each of these functions are so different that they're very difficult
  to integrate on a silicon substrate. Some vendors are facing the challenge
  head-on by trying to integrate them anyway, while others are looking to new
  packaging technologies that combine multiple chips with multiple functions into
  a single module.

sudhang 's Library tagged no_tag → View Popular

HOWTO: Be more productive (Aaron Swartz's Raw Thought)

Share the load

IEEE Spectrum: How We Found the Missing Memristor

IEEE Spectrum: Multicore Is Bad News For Supercomputers

The Future of Photography - TIME

Paxos - Pinewiki

Ars Technica Guide to Virtualization: Part I: Page 3

Ars Technica Guide to Virtualization: Part I: Page 2

The Texas Tech Tornado Cluster

Ars Technica Guide to Virtualization: Part I: Page 1

Natasha Demkina - The Girl with Normal Eyes

How To Become A Hacker

Distance-vector routing protocol - Wikipedia, the free encyclopedia

Selective Repeat Protocol

Unqualified Reservations: A straightforward explanation of the present financial crisis (part 1)

Three Way Handshake

Constraint Guide - Binarization

Constraint Guide - Constraint Satisfaction

PsyBlog: How to Improve Your Self-Control

Constraint Guide - Introduction

Classic.Ars: Understanding Moore's Law: Page 6

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