Macbook Air difference between two models?
My lovely other half has offered to buy me a Macbook Air - my question is (being an ignoramus) what is the difference between the model having a 80GB 4200-rpm PATA hard drive and the much more expensive model with 64GB solid-state drive.
can anyone explain in simple terms?
Thanks
Hi,
I hope simple enough ;-):
a) 80 GB 4200 rpm PATA model: This model uses a regular hard disk drive to store long-term data. This means, there are a couple of thin glass disks spinning at 4200 rpm. These glass disks hold a thin metal layer that is magnetized in either one or the other way. That way the computer can store data like your files or the operating systems files for long-term retrieval. The disk is rewriteable.
b) Same usage principle for the SSD model. The difference is, no moving parts, no glass disks, but small "ic-chips" storing the data just like the memory (RAM) of your computer does use. The difference to the RAM is that the data is not forgotten on power down, like with the glass disks.
The pro's of b) are less heat, no moving parts, faster access. The con's limited size (only 64 GB) and more expensive. If I would be you, I would take the HD version and ask for an external hard disk or even a TimeCapsule (for wireless Time Machine backups).
Volker
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Hi,
I have a question about the data type of the difference between two date type of datas.
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END
FROM SSHIPMENTS;
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I don't know if the data type of the interval is wrong.
Many Thanks,
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TYPE t_col
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INDEX BY PLS_INTEGER;
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j NUMBER := 0;
l_sql VARCHAR2 (2000);
col1 VARCHAR2 (30);
col2 VARCHAR2 (30);
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val2 NUMBER;
status VARCHAR2 (30);
CURSOR c1
IS
SELECT column_id, column_name
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BEGIN
FOR i IN c1
LOOP
j := j + 1;
l_col (j) := i.column_name;
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LOOP
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);Thanks for every reply. Please kindly correct me for any mistake.Let us define an elementary operation as one of
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The distance measure described in the above post is called the edit distance, or "Levenshtein distance". If you google that, you're bound to find some ready-made java code that does it for you.
Happy hunting!
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P Prakashyou could try something similar to this, for each table pair that you want to compare:
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Hi All,
My first time here and really new to programming. I would like to get the difference between 2 columns that are inside
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PeriodNumber
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2) Receivables 12,000 11,500
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Total Assets 27,000 32,000Hi yabgestopa,
From your description, you want to get the difference between two columns in a column group. After testing it in my environment, we can use custom code to achieve your requirement. For more details, you can refer to the following steps:
Copy the custom code below and paste it to your report. (Right-click report>Report Properties>Code)
Dim Shared Num1 As Integer
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Public Function GetAmount(Amount as Integer, Type as String)
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End If
Return Amount
End Function
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Right-click the second column to insert a third column with Outside Group-Right.
Then use the expressions below in the matrix.
=Code.GetAmount(Fields!Amount.Value,Fields!PeriodNumber.Value)
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The report looks like below.
If you have any questions, please feel free to ask.
Thanks,
Katherine Xiong
Katherine Xiong
TechNet Community Support -
Better estimation of phase difference between two signals with variable frequency!
Hello LabView Gurus,
Being a power engineer and having just a little knowledge of signal processing and labview, I have been pulling my hair out for the last couple of days to get a better estimation of phase difference between two signals.
We have two analog voltage signals; 1. sine wave (50Hz ± 1Hz) and 2. a square wave with exactly half of sine wave frequency at any time.
At the starting point of operation (and simulation/acquisition) both signals will have no phase difference. However, the square wave's frequency changes unpredictably for a just a few millisecond but then it gets synchronized with sine wave's frequency again. This means that the square wave will be phased out from its original position. The task of the labview is to find the phase difference between the two signals continuously.
My approach to determine the phase difference is to measure the time when sine wave crosses zero amplitude and the time when the very next square wave changes amplitude from zero volts to +ve voltage (I have a 0.5volts threshold just to avoid any dramas from small line noise). The difference between these times is then divided by the time period and multiplied by 360 to get this phase difference in angles.
As this part is just a small block of a big project, I can only allow 5000Hz sampling rate each for both signals. I read 500 samples (which means I read data from 5 cycles of sine wave and 2.5 cycles of square wave).
Now the problem is, as long as the frequency of sine wave stays constant at exactly 50Hz, I get a good estimation of the phase difference but when the frequency changes even a little (and it will happen in the real scenario i.e 50Hz ± 1Hz and the square wave's frequency is dependent of sine wave's frequency), the estimation error increases.
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You can observe that the estimation error increases after you push the button.
All I need to do is to reduce this estimation error and make it as close to the actual phase difference as possible. Any help would be greatly appreciated.
I am using LabView 2009 for this task.
The application is for electric machines and the stability/performance of machines under different faults.
Thank you for reading this far!
Regards,
Awais
Attachments:
v603.png 320 KB
v603.vi 186 KBJeff Bohrer wrote:
Basic math gives me a bit of pause on this approach. You are sampling at 50 times the frequency of interest so you get 50 samples per cycle. your phase resolution is 1/50th cycle or 7.2 degrees +/- noise. You will need to samlpe faster to reduce phase resolution or average multiple readings (at a time cost that is signifigant)
Jeff- (Hardly Working)
I am sampling at 100 times the sine wave's frequency and 200 times the square wave's frequency. Increasing the sampling rate completely solves my problem. But since I am acquiring several other inputs, I cannot afford a sampling rate higher than 5kHz.
F. Schubert wrote:
I'm not a signal processing expert, but here my basic understanding.
If you simulate sampling with 5kHz and a frequency of 50 Hz (and both are 'sync' by design), you always get an exact 5 periods. Any variation of your signals frequency gives you a propability to get 4 or 6 'trigger' events. That's an up or down of 20%!
The one measure to reduce such problems is using 'window functions'. They don't fit your current approach (counting instead of a DSP algorithm), so this needs to be reworked as well.
My approach would be to use the concept of a Locki-In amplifier. You need to phaseshift your ref-signal by 90°. Then multiply your measurement signal with the ref signal and the phase shifted ref signal. The obtained values for x/y coordinates of a complex number. Calculate the theta of the complex number (with the LV prim). Feed this in a low pass filter.
The trick on this is, that the square wave has harmonics in it, in this you are interested in the second harmonic which is the sine wave.
To get rid of the effect that the sync between sampling rate and ref signal frequency gives an error, you then can use the window I mentioned above (place it before the lock-in).
For a design that really plays well, use a producer-consumer design pattern to get the calculations done in parallel with the DAQ.
I suggest you to check on wikipedia for some of the keywords I mentioned. Go also for the external links which lead to great tutorials and AppNotes on the signal processing basics.
Sorry, it's not a simple solution I offer and we will have quite some conversation on this forum if you follow this path. Maybe someone else knows a simpler way.
Felix
www.aescusoft.de
My latest community nugget on producer/consumer design
My current blog: A journey through uml
An interesting view. the sine wave can indeed be looked as a second harmonic of the square wave. I will implement your idea and get back to you as soon as I get some results. But since I have very limited knowledge of signal processing, it might take me a while to get my hear around the solution you mentioned. -
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please help.DECLARE @from datetime
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Best Regards,Uri Dimant SQL Server MVP,
http://sqlblog.com/blogs/uri_dimant/
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Hi all,
I need to do a difference between two date using formula variable processing type customer exit beaucause I must use factory calendar in the formula.
How can I do it?
Can you give me an example of the routine?
Thanks a lot
GianmarcoHi,
You can still use the same code to copy it and customize as per your need. All you need to do is to subract the dates using the class: CL_ABAP_TSTMP after converting to timestamp and resulting seconds you convert back to days....Please get help from the developers to do this...
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Cheers,
Emmanuel.
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